A Psyker is an individual of any intelligent species in the Warhammer 40,000 universe who possesses some degree of psychic ability or powers. Psychic powers are sometimes referred to as "sorcery" and their users as "witches" in the Imperium of Man and among the Eldar, particularly when such powers are used in such a way that they show no regard for the dangers they may spawn for others or are used in pursuit of the agenda of the Chaos Gods.
Psykers draw their powers from the extradimensional realm known as the Immaterium or the Warp that underlies four-dimensional realspace and is the source of all psychic energy in the universe. As such, psykers, particularly human psykers whose minds are far less disciplined than their Eldar counterparts, are often in danger of possession by the daemonic entities of the Warp, insanity and ultimate corruption by the Ruinous Powers of Chaos.
Psykers of the Galaxy
Most of the intelligent races in the Warhammer 40,000 universe employ psykers on the battlefield; some of these psykers are inevitably more potent than others. There are three exceptions to this: the Tau, the Dark Eldar and the Necrons. The Tau have yet to develop any psykers among their race because they have only recently evolved to fully sentient status. The Dark Eldar, though as possessed of inherent psychic ability as their Craftworld counterparts, fear that the use of psychic powers only further hastens the loss of their souls to Slaanesh. The Necrons no longer possess souls since they transferred their consciousnesses into their necrodermis bodies and became creatures wholly of the physical universe like their C'tan masters; as a result they no longer generate any presence within the Immaterium and cannot draw upon any form of psychic energy from that realm.
The Imperium of Man
The genetic mutation which grants a human being the ability to draw upon the psychic energy of the Immaterium has become increasingly common since the Neolithic Age. This change is the harbinger of Mankind's slow evolution into a fully psychic species much like the Eldar who will be more intelligent, more capable and ultimately more peaceful than humanity is at present. Unfortunately, this process has been quite uneven and even the most powerful human psykers still have minds that have not developed to the point that they can touch the Warp with the level of control wielded by the Eldar Farseers. As such, because of this lack of mental development and Mankind's own still deeply flawed, covetous nature, most human psykers always run a substantial risk of being possessed by the daemonic entities of the Warp and spreading the death and destruction of Chaos wherever they go. It is for this reason that the Emperor of Mankind largely banned the use of psychic powers throughout the Imperium of Man save in a few notable exceptions at the Council of Nikaea during the Great Crusade. Psykers, although justifiably feared throughout humanity's history because of their extraordinary powers and the equally extraordinary dangers they sometimes unleashed on those around them, serve several vital roles within the Imperium today under the exceptions laid out by the Council of Nikaea some ten millennia ago.
Psykers are too dangerous to remain at liberty on the Imperium's myriad worlds; their minds are susceptible to daemonic possession as their strong presences in the Warp can serve as gateways into the material universe for all kinds of Warp entities if they are weak or undisciplined with their powers. Uncontrolled, they can intentionally or unintentionally cause the destruction of entire worlds and have done so in the pre-Imperium past, such as during the terrible days of the Age of Strife. Humans found to be bearing the psychic mutation, if they are not simply killed, are sent to Terra aboard the infamous Black Ships which endlessly traverse the Imperium.
All human psykers have an ordained role as servants of the Imperium if they have the willpower to control their abilities and not become a danger to others. Their exact role depends on the psychic powers they manifest and their strength of character and will, though psykers who have some use for the Imperium are known as Sanctioned Psykers while individuals who manifest unusually strong psychic powers often become known as Primaris Psykers, the most powerful human psykers in existence.
Psykers serve within the Imperial Guard and the Space Marine Chapters, employing their powers in battle as well as for civil duties. Imperial Navigators use their psychic "third eye" to cross safely through the Immaterium using the faster than light Warp-Drive employed by all Imperial starships. Astropaths provide faster than light communication as their telepathy is not confined to the speed of light since messages travel through the Warp much as starships use the Warp to make interstellar jumps. Thousands of psykers are sacrificed every year to sustain the Emperor's psychic presence in the Warp, and thousands more must constantly be drained to power the Astronomican, which broadcasts an enormous homing signal through the Warp which is used as a point of reference by starship Navigators. However, the Imperium of Man also ruthlessly executes countless less-fortunate psykers who are seen as mutants, heretics, potential threats to their homeworlds, or gateways to the daemons and corruption of Chaos.
Psykers first emerged amongst Mankind in the middle part of the long distant Age of Technology, a period of human history about which all but nothing is remembered in the 41st Millennium. Since that time, ever-greater numbers of humans have been born with the ability to wield psychic powers, and others still come into such powers later on in life. This phenomenon has been the subject of study, debate, superstition, intolerance, and even open warfare throughout the ages, and all manner of meanings have been read into it. Some claim that Humanity is undergoing the birth pangs of a new phase in its evolution, and can look forward to an age when the entire race transcends to an entirely different level of existence. Most interpretations are far less optimistic, however, and those with knowledge of such things point to the fate of the Eldar as a warning of what doom awaits Mankind. Others still hold that this gradual and ever-increasing evolution is the doing of the Emperor himself, who exists to shepherd the entire species into its new age. Those of a notably Puritan persuasion hold that for every psyker born, a thousand twisted mutants are spawned first, as if the process itself was abhorrent to the Emperor, to nature or to both.
Whatever the truth of the matter, it is evident that more and more psykers are being born or coming into their powers with every passing generation. The bleak holds of the Black Ships grow ever more bloated with those swept up in the psyker culls. With this increase, the risk of Daemonic incursion and Enslaver plague grows worse, for should one powerful psyker go undetected, the slavering denizens of the Warp might breach reality itself and come pouring in, bringing the doom of humanity with them.
Astropaths (short for Astro-telepath) serve throughout all the Imperium's many governmental divisions and make up a communication network designed to transmit and receive psychic messages through interstellar space. New Astropaths are chosen from the multitudes of psykers who are born across the Imperium every year and brought to Terra on the Black Ships due to their great power. Once chosen, Astropaths receive psychic training by the Adeptus Astra Telepathica's teaching division which is known as the Scholastia Psykana, before they are "soul-bound" to the Emperor. This psychic ritual transfers some of the Emperor's vast power -- and more importantly, his mental control -- to the psyker. Such an experience is quite physically traumatic for the psyker and not all survive or maintain their sanity. Even the survivors suffer damage to their physical senses, especially their eyes, so that almost all Astropaths are blind, their optical nerves burnt out during the soul-binding process. Their increased psychic senses, however, tend to make up for this loss of sight and most Astropaths have the uncanny ability to see everything just as well as a sighted person despite their lack of vision.
Being joined with the Emperor is necessary, as it greatly increases Astropaths' already formidable powers, granting them full control over the ability for which they were chosen - the transmission and reception of psychic messages across hundreds of light-years of space. Due to the draining nature of their job and the costs incurred by soul-binding, many Astropaths are physically frail and can die quite young due to sheer mental exhaustion.
Some of the psykers recruited into the Adeptus Astra Telepathica are trained to serve within the Astra Militarum as Sanctioned Psykers rather than as Astropaths. These psykers may draw upon the power of the Warp, unleashing it upon their enemies as a weapon. They are also called upon to advise high-ranking Imperial Guard officers, though with varying degrees of success. Their limited training and equipment leads them to be more vulnerable to the perils of the Warp than the much more powerful psyker Librarians of the Space Marine Chapters. Each time a Sanctioned Psyker utilises their power, they put themselves at considerable risk and are prone to have their minds destroyed in the process. Some Psykers in rare cases have even literally exploded from overloading their bodies with Warp energy, taking out entire Guard squads nearby. That aside, they are still a potent force when deployed and used properly. On the battlefield, Sanctioned Psykers can advise an officer and guide their command, protect him from psychic attack, or fire bolts of lightning from their hands. Despite their use, Sanctioned Psykers are at best tolerated, and at worst loathed, by their companions. They are never allowed to stray far from the ever-watchful gaze of the regiment's Commissar, who can and will execute the psyker at the slightest sign of Warp taint, "for the psyker's own good!" The fact that many Sanctioned Psykers meet their demise at the end of a Commissar's Bolt Pistol has earned them the dubious nickname of "bolt-magnets" amongst the rank-and-file soldiers of the Guard.
If a Sanctioned Psyker manages to survive a term of service in the Imperial Guard, he will be returned to the care of the Adeptus Astra Telepathica, who will then test the veteran psyker thoroughly for mental fortitude and psychic might. If the psyker survives those tests, he will be trained to become a Primaris Psyker, and taught how to harness the power of lesser psykers and make it subservient to his own. When he rejoins the Imperial Guard, the Psyker Primaris will be able to form a "circle" or "coven" with other Sanctioned Psykers. With the power of the circle at his disposal, the Psyker Primaris' precognitive predictions will be more accurate, his protective wards and abjurations more potent and his psychic attacks more devastating. And yet, for all his might and utility to the Imperium, even a Psyker Primaris is not spared the suspicious gaze of the Commissar, and he too may one day find himself executed by a Bolt Pistol shot swiftly and surely delivered.
Psykers are employed by the Adeptus Astartes in the form of their Chapter Librarians. These individuals are chosen from among the most powerful psykers in the Imperium. Librarians are responsible for maintaining the records of the Chapter they belong to, hence their name, and they can also use their talents to discern which psychic mutants are dangerous and which can be utilised by the Imperium as Sanctioned Psykers, Astropaths, and even new Librarians. Librarians, having much better equipment (a Psychic Hood, etc.), willpower, protection and training, as well as the genetic enhancements of a Space Marine, are much less prone to falling prey to the perils of the Warp than other Imperial psykers. On the battlefield, Librarians are fearsome opponents, able to unleash devastating psychic powers and psychically augment their own physical prowess. They are also skilled at defending themselves and their Battle-Brothers from psychic attack.
Though they are tasked with hunting down rogue psykers and collecting latent ones for training to aid the Imperium among many other duties, many members of the Inquisition are psykers themselves, Inquisitor Gideon Ravenor being an especially potent example. Like so much about their organisation, one Inquisitor's psychic abilities can vary greatly from another's. Some specialise in unleashing torrents of fire and other direct psychic weapons, while others, like Inquisitor Gregor Eisenhorn, specialize in powers that aid them in interrogations or to fool an enemy into stepping out from cover, dropping his weapon, or any number of other subtle "mind tricks."
The elite Grey Knights Space Marines Chapter that serves as the Chamber Militant of the Inquisition's Ordo Malleus, the Daemonhunters, is wholly made up of psykers: being a psyker is a condition for recruitment into the Chapter. Due to the entire Chapter being composed of psykers, the rigorous process for becoming a Space Marine is made even more difficult, as all Grey Knight Battle-Brothers have no memory of their past and many fail before their gene-seed implantation can be complete. However, the rigorous selection process and memory-wiping techniques employed by the Grey Knights to rid their recruits of those common human frailties that the Ruinous Powers can prey upon to corrupt an individual has proven extraordinarily successful, for not a single Grey Knight has ever turned to Chaos, despite their psychic abilities making them more vulnerable than standard Space Marines.
Among all the intelligent races of the galaxy, the Eldar possess some of the most powerful psykers in existence, using their ability to divine the future to shape their fate while also unleashing devastating telekinetic powers upon those that oppose them; however, the sheer power they generate when they combine their psychic strengths ensures they must be cautious to not attract the attention of Chaos and the other predatory entities of the Warp. They are forced to become highly disciplined and regulated in their usage of psychic power. Eldar psykers come in the form of either Farseers or Warlocks, the former being the more powerful psykers of the two. Farseers will lead an Eldar warhost against the enemy and shape the course of battle with their powers. Warlocks, former Eldar Aspect Warriors who possess potent psychic powers because they have begun to walk the Eldar Path of the Seer, typically serve as bodyguards for the Farseers and possess lesser, usually defensive-oriented psychic powers. The Ulthwé Craftworld is said to possess the greatest number and the greatest quality of known Eldar psykers due to its proximity to the Eye of Terror. They can divine much further into the future and with better clarity than the Farseers of the other Craftworlds. The Craftworld Iyanden has a variant of Warlocks called Spiritseers. They differ very little from their normal counterparts, save to guide all of those Eldar constructs that are empowered by the souls of fallen Eldar encapsulated within Spirit Stones. Spiritseers will guide Eldar Wraithguards in combat, better directing those Wraithbone constructs' awesome firepower for optimum efficiency.
Forces of Chaos
The Forces of Chaos host a great many mutants among their number, including many with psychic potential. Chaos psykers, often called Sorcerers, can perform various tasks such as summoning daemons and unleashing devastating weaponised psychic powers upon the enemy. The Chaos God Tzeentch is devoted to sorcery; Chaos Space Marine Legions worshiping Tzeentch such as the Thousand Sons possess a large number of psykers that can aid in battle. Other Traitor Legions such as the World Eaters denounce sorcery and psychic ability in favour of the wanton bloodshed of close combat. The Iron Warriors Traitor Legion often also sneers at the use of sorcery. Chaos Sorcerers can unleash potent powers and are fearsome individuals, often mutated beyond recognition. Tzeentch-worshipping Sorcerers are especially potent, able to perform feats that would leave even an Eldar Farseer making sure his Spirit Stone is firmly within his grasp.
- "Too much noise! Too much! I fink I'z gunna...I'z gunna...WAAAGH!"
- — Weirdboy Gazrog
The Orks are an innately psychic species and they unconsciously generate a considerable amount of psychic "background noise," a psychic energy field known simply as "Da WAAAGH!" This field of gestalt psychic energy grows more potent and more intense when the Orks themselves are excited, particularly during battle, creating an almost palpable tension that accompanies Ork hordes. Weirdboyz are the psykers of the Ork species, absorbing the energy of Da WAAAGH! and expelling it in violent surges of luminescent green power. Weirdboyz have little control over their abilities, and as the potency of this energy increases with the number and enthusiasm of the Ork Boyz around them, so does the power that a Weirdboy must endeavour to control. Even when they manage to contain this violent and erratic force, bizarre phenomena commonly accompany Weirdboyz, ranging from flashing lights and strange noises to psychokinetic tremors and random fires. Should they fail to disperse, direct or emit this energy in some controlled manner, a Weirdboy may cause even more dramatic phenomena, such as the explosion of nearby Ork heads. This is known as a " 'Eadbang" when the power is not discharged safely. Weirdboyz are also found in Feral Ork armies, where they are known as Wyrdboyz. Warpheadz are those Weirdboyz that -- unlike normal Weirdboyz -- have survived enough battles for their minds to become saturated with the power of the Warp, and actually revel in and enjoy the use of their powers.
The Necron cannot make use of psykers because, though a once-living race, they chose to have their living consciousnesses interred by the C'tan into Necron constructs for immortality at the cost of their souls. Since a soul is simply an individual's psychic imprint on the Immaterium, the Necrons are no longer capable of accessing its psychic power. The Necrons are now living machines, beings of pure material like their masters who leave no impression on the Immaterium. The C'tan are described as creatures entirely born of the material realm, and thus they cannot sense or influence the Warp in any way. Thus they hate and fear the Immaterium and all things strongly connected to or influenced by it such as psykers. The Necrons are notable for utilising technology specifically designed for destroying psykers, most prominently the Pariahs. Necron Pariahs are an elite bodyguard that terrify any psykers in their proximity since no member of this group possesses a Warp signature and thus a soul. These Necrons, all of whom were once human psychic "blanks," share the "pariah gene" in common with the Imperial Assassins of the Culexus Temple of the Officio Assassinorum, and both groups are the soulless victims of the insertion of the gene millions of years ago into the proto-human gene pool by the C'tan in the hope that they could be used as living weapons against the Old Ones and their psychic servant races like the Eldar. The C'tan would sooner feed off the thermonuclear power of a sun than deign to consume a single soul with its foul taint of Warp energy. Hatred of the psychic does not bar some contradictory evidence about the Necrons' use of psychic abilities, as seen when the Necrons emitted a fear-inducing telepathic ability, from which the Commissar Ciaphas Cain was saved only because of the presence of a "psychic blank" with the pariah gene in the vicinity.
The alien race of the Tyranids is one of the most psychically active races in the galaxy, if not the most, with every single Tyranid telepathically connected to all other members of its species through the psychic gestalt that is called the Hive Mind. It is suspected that this constant and massive "psychic traffic" is what causes the Shadow in the Warp, a phenomenon that makes Warp travel and astropathy almost impossible in the vicinity of a large Tyranid Hive Fleet. Though the lesser Tyranid biomorphs have no psychic abilities of their own, the larger Tyranid Warriors act as focal points for the Hive Mind called synapse creatures, capable of mind-controlling all of the lesser Tyranids around them. Zoanthropes, creatures supposedly created by combining Tyranid DNA with DNA from other psychically active races like the Eldar, are extremely powerful psykers. Their bodies have devolved into little more than a humongously bloated head attached to an atrophied, fetus-like body incapable of even moving on its own power, therefore requiring the creature to use its psychic abilities to levitate across the battlefield. Hive Tyrant are also very powerful psykers, although not as powerful as Zoanthropes, and act as the core of the Hive Mind within the Tyranid swarms. Larger Tyranids, such as Dominatrixes and the mysterious Norn-Queens, are also psykers of immense power, though the full extent of their abilities is a matter of speculation within the Adeptus Mechanicus.
The Tau have no known psykers. In the video game Warhammer 40,000: Fire Warrior, it is revealed that the Tau are naturally resistant to the mutating effects of Chaos, having almost no psychic presence in the Warp at all, though they are not soulless like the Necrons. However, this did not prevent the Tau Ethereal, Ko'Vash, being blasted apart by a burst of Chaos energy. It is rumoured that the Ethereals are capable of utilising Warp power, as it is suggested that this is how they are able to cause such loyalty to the Greater Good in all of the Tau, although it has been discovered by Adeptus Mechanicus researchers that the members of the Ethereal Caste possess a large, diamond-shaped scent-emitting organ in their head which may allow them to control other Tau through the emission of pheromones.
Although the powers of Psykers are many and varied, they usually fall into one of several disciplines. The five most common psychic disciplines are: Biomancy, Divination, Pyromancy, Telekinesis and Telepathy. Each discipline has a particular character, which is reflected by the powers within it. The Telepathy discipline, for example, is grounded in mind control, and its powers act through compelling and influencing the thoughts and actions of others. It should be noted that, whilst two different psykers may both use the same discipline, their powers are likely to manifest in unique, idiosyncratic ways. So for example, an Imperial psyker using the Pyromancy discipline may hurl blazing bolts shaped like an avenging, two-headed eagle whilst a corrupt Chaos Sorcerer might conjure multi-hued conflagrations of living Warp fire and an Ork psyker or "Weirdboy" could vomit cones of billowing green flames. Many of the other alien races and even different Imperial factions' psykers such as Astra Militarum Wyrdvane Psykers or Space Marine Librarians also have access to their own, unique psychic disciplines and powers beyond what is listed here.
Some psykers specialise in only one discipline, honing a few powers to the exclusion of all others. Others manifest a much broader range of psychic disciplines and abilities -- in such cases, the psyker will be able to generate powers from several psychic disciplines.
Biomancers specialise in manipulating biological energy and processes with the power of their minds. They are masters of the flesh, learning to shape and influence the physical forms of themselves, their allies or their enemies, according to their will.
- Smite - Lethal bolts of bio-lightning leap from the psyker's fingertips, tearing his foes apart.
- Iron Arm - By transmuting his flesh into living metal, the biomancer can wade through enemy fire unscathed and pulp skulls with his bare fists.
- Enfeeble - As the psyker channels his powers, tendrils of Warp energy lash over his victims, every caress sapping vitality from their bodies.
- Endurance - Reaching into the essence of his allies, the biomancer knits together bones, heals flesh and banishes fatigue so that they carry on the fight.
- Life Leech - With a twist of his gnarled hands, the wrathful psyker rips the life force from his enemy, hoarding the stolen essence and using it to reinvigorate and restore his own injured flesh.
- Warp Speed - The powers of the Immaterium flow into the psyker, heightening his speed to supernatural levels. A blur is he amongst his enemies, felling the unrighteous with blows too swift to see.
- Haemorrhage - Focussing his mutant mind, the psyker reaches forth and sets a fire within his victim's flesh. Within moments, the unfortunate foe's blood begins to boil in its own veins, tearing him asunder as it bursts from every pore.
Diviners seek to discern the hidden past of the galaxy and know the course of events yet to come. These abilities allow diviners to look into the twisting strands of the Immaterium in search of the answers they seek, and sometimes even influence the outcome of fate itself.
- Prescience - The psyker can effortlessly predict the paths of bullets and swords. By focussing his Warp-sight even more closely, he can guide his allies' aim, bringing a swift and merciless death to their foes.
- Foreboding - Thanks to his Warp-gifted insights, the psyker and his allies are aware that their foes are about to charge, even before the foes themselves have realised it.
- Misfortune - With a click of his fingers, the diviner twists fate so that his followers' blows punch through the weakest points in their opponents' armour.
- Perfect Timing - As soon as his consciousness pierces the veil of the Warp, a rush of images floods the diviner's mind, foretelling the actions of his enemies, down to the merest microsecond. Armed with this information, the diviner's allies can predict exactly when their foes will peer out from behind cover and expose themselves to a lethal head shot.
- Precognition - Having already witnessed the one true path to victory, the diviner strides across the battlefield like an avenging god of war. Whilst the premonitions run true, he is all but undefeatable, proof against bullet and bolt, blade and bombardment. However, should his self-wrought prophecies fade, or turn false, he will surely be doomed to ignominious defeat.
- Scrier's Gaze - The diviner can see the battlefield clearly in his mind's eye, with the vantage point of a hunting hawk and the precision of a laser. The to and fro of armies and war machines is but the scurrying of ants beneath his omniscient gaze. Thus can the diviner direct exactly when and where they are most needed, leaving no clue behind as to how this trickery was achieved.
A pyromancer is a master of fire and flame, a psyker who is able to create searing infernos out of thin air. Pyromancy is one of the most spectacular and destructive forms of psychic ability, and those who face a pyromancer in combat are oft reduced to nought but a pile of charred bones.
- Flame Breath - A torrent of psychically-generated flames pour forth from the psyker's eyes and mouth, engulfing the target.
- Fiery Form - Bullets and shells pass straight through the pyromancer as he transforms into an incandescent being of living Warpfire, striking out at his foes and setting their souls ablaze.
- Fire Shield - With a sweep of his arms the psyker throws up a towering wall of flame to protect his allies.
- Spontaneous Combustion - Focussing his anger, the pyromancer can melt or incinerate his foes in a heartbeat. Yet when his rage boils over, the unfortunate victim's body explodes in a blast of ash and roaring flame. Who can say how many will fall victim to his wrath before it is sated?
- Sunburst - The psyker sings a wild song whose notes were old when the universe was young. As he does so, an incandescent aura appears about him, growing ever brighter and hotter with every refrain. Only when the song is ended does the aura explode, discharging its pent-up fury in a blinding, supernoval flash.
- Molten Beam - The pyromancer claps his hands together and turns them outward towards the foe. As he does so, a white-hot beam of blazing energy bursts from his palms. It melts armour to slag and vaporises flesh, leaving only ghastly shadows in its wake.
Telekines are able to manipulate the material world with the power of their minds, translating sheer mental power into physical force. These psykers can lash their foes with psychic energy, erect invisible force shields to protect themselves and even rend apart the fabric of reality.
- Assail - Using nothing but the power of his mind, the psyker tears a boulder or rock from the ground and hurls it at the foe.
- Crush - By reaching out his arm and clenching his fist, the psyker entraps his foe in a choking and crushing mass of psychic force. Gritting his teeth, the psyker continues the assault until flesh, armour and bone alike are ground to powder.
- Gate of Infinity - The psyker punches a corridor through the roiling Immaterium, allowing him to cross great distances in the blink of an eye.
- Objuration Mechanicum - Weapons jam and engines seize up as the telekine uses his powers to wrench and twist the inner workings at the hearts of nearby machines.
- Shockwave - The psyker slams his palms together and the noise is magnified a hundredfold, releasing a shockwave that snaps bones and knocks foes off their feet.
- Telekine Dome - Bullets bounce off of thin air and are deflected alarmingly towards friendly forces as the psyker erects a barrier of shimmering psychic energy about himself.
- Vortex of Doom - The telekine opens a tear between the material realm and the howling destruction of the Warp, unleashing energies that utterly consume his foes.
Telepaths are psykers whose mental expertise lies with contacting and controlling the minds of others. With a single thought, a telepath can blast away his foe's sanity, induce states of numbing terror or possess his victim's thoughts and mould their actions as if they were his own.
- Psychic Shriek - The psyker breathes in deeply the power of the Warp before emitting a banshee howl of psychic energy that shreds the minds of his enemies.
- Dominate - The psyker reaches into his foe's mind, tramelling his soul and crushing his will to fight on.
- Mental Fortitude - Despair is turned into fresh hope and courage into insane heroism as the telepth projects inspirational thoughts of victory into the minds of his allies.
- Puppet Master - The telepath possesses his victim's mind, controlling their movements, their aim and their trigger fingers as if they were marionettes.
- Terrify - Even the bravest of heroes quake in terror as the telepath assailts them with images from their own darkest and most dreadful nightmares.
- Invisibility - Reaching into the minds of his foes, the psyker obscures himself and his allies from the enemy's visual line of sight.
- Hallucination - Paranoia, confusion and panic are heightened to a debilitating degree as the telepath alters his foes' perceptions of reality, creating fearful visions, confusing or befuddling the enemy, or even generating the belief that their fellows are the true enemy.
There are different grades used to incrementally rank the power of a psyker within the Imperium of Man, ranked from the most powerful to least powerful, top to bottom:
- Alpha Plus
The grades continue on down through the letters of the Greek alphabet. Grade Sigma and below are levels of "anti-psychic power". Such people are more commonly known as "psychic blanks" since they cannot be detected, manipulated or affected by psychic means and possess the Pariah Gene.
The psychic power the top four grades represent is immense. A high Delta level can read the minds of all the people in a good-sized town simultaneously, or crush a man to death against a wall in seconds. High-grade psykers are extremely powerful, and not to be taken lightly. Beta grade is the highest level of psychic power that a human can attain and still be considered sane.
An Alpha Plus grade psyker, however, is a being of almost grotesque power. They are described as being able to "turn a man inside-out with a glance," "snap a Battle Titan in half with a flick of the wrist," and "a muttered syllable can turn an army upon itself in a frenzy of blood lust." They are capable of destroying entire worlds -- sometimes unintentionally.
There is some controversy as to whether this depiction should be taken as an objective description of the Alpha level of psychic mastery, or if it is intended to be read as Imperial propaganda, and just the exaggerated view of the generally anti-psychic authorities of the Imperium. The Alpha grade psyker Esarhaddon is powerful enough to control hundreds of Imperial citizens as puppets, but he is not described as being powerful enough to destroy a Battle Titan, and is eventually subdued.
However, there are very few Alpha or Αlpha Plus psykers that can be controlled safely, or even at all. Because more powerful psykers attract proportionally more interest from Warp-bound daemons, many are driven insane, tainted by Chaos, or even become possessed (examples include the Apex Twins, who were responsible for murdering scores of Astra Militarum regiments). They are one of the biggest threats the Inquisition has to face, and are one of the grave dangers to Mankind that the Ordo Hereticus was formed to combat. Most such psykers are executed, as the threat they pose is simply too great to deal with or control to any large degree. The Inquisitor Gideon Ravenor was known to be an Alpha Plus psyker, but was later downgraded to the grade of a powerful Delta or weak Gamma. The Emperor of Mankind would be considered an Alpha Plus psyker, though in fact His power is so great that it probably cannot be measured by any mortal scale.
An example of a Beta level psyker is Sergeant Agun Soric, an Imperial Guardsman who served in the Tanith First and Only Regiment. He was able to detect blood poisoning in a fellow trooper, but his most prominent power was his ability to write messages to himself, which are contained in a brass message shell. Even after throwing the shell away, he would soon find it wriggling in his pocket, containing a message written in his own handwriting. At first the messages contained advice or warnings, but soon began to include criticism as he began to realise what he was, and the danger he posed as an untrained psyker. He eventually admitted his abilities to his regimental commander Ibram Gaunt and was taken by the Inquisition's Black Ships. He was later revealed to have become the Sanctioned Psyker of the 51st Cadogus Armoured Regiment, and was able to use his abilities to manifest from the Warp the ghosts of dead Tanith soldiers. Most notably, he created a ghost of the Cadogus Regiment's Major Berenson and his aide, who the First-and-Only thought to be a normal soldier rather than a Warp echo. Berenson was later "killed" in a Valkyrie crash. When Commissar Hark, who was also involved in the crash, told the colonel of the 51st Cadogus that Berenson had been killed, the colonel replied that Major Berenson's Valkyrie had actually been shot down en route to meet with the Tanith 1st five solar days before! Soric was later mercy-killed by Commissar Hark, but told Hark before his death that what he had been using his ability for was to inform the men of the Tanith 1st that Colonel-Commissar Gaunt was still alive -- he had been captured and tortured by the forces of the Blood Pact.
The Imperium has at times employed a different system of measuring psychic ability, where an individual's psychic profile is represented by a decimal value, presumably from 0 to 1, instead of using the Greek alphabet system.
Every psyker of every species possesses the ability known within the Imperium of Man as the "Witch-Sight" or "witchsight." Because psykers draw on the power of the Immaterium for their abilities, they can see the corona of psychic energy that surrounds every living being in realspace. For sentient beings, this means being able to glimpse the nature of any psychically unshielded person's psyche -- their psychic "aura" in ancient Terran terms. Every psyker's mind interprets or experiences this information differently based on the nature of their own cultural and mental constructs. However, the one constant experienced by all is that people whose psyches are riven by the darker emotions and motivations appear in Witch-Sight as degraded monsters, while those of the opposite persuasion appear as pure or even angelic beings. Psychic Blanks are those rare individuals who possess no presence in the Immaterium and thus are immune to being affected by psychic abilities, such as those humans who inherit the Necron-engineered Pariah Gene. When seen by Witch-Sight, the perception of a Blank usually causes an adverse, almost painful reaction in psykers, since they do not possess an aura of any kind and therefore register as psychically disorienting. Eldar psykers are known to possess much more penetrating Witch-Sight than even the most powerful of their human counterparts.
Several types of anti-psyker weaponry have been developed by the Imperium, Necrons and other races to counter psykers. For the Imperium, these include the Culexus Assassins and their Psykout weapons, which have devastating effects on psykers. Weapons include the Psycannon, Warp Swords, and the use of other psykers.The Necrons have developed the Cadian Pylons that, once their network is complete will completely separate the Warp from the material universe, thus rendering psykers powerless. On a smaller scale there are the Pariahs, Necrons made from humans with the pariah gene - this makes them, like the Culexus Assassins, soulless, and severely debilitating to nearby psykers. Lastly, the Dark Eldar, while not having any known psykers among their ranks, have developed weapons designed for psyker destruction to be used against their hated Craftworld Eldar counterparts. One of the most gruesome (and rare) is the Crucible of Malediction, a nightmarish device which contains the essence of a slain psyker tortured into insanity. When the Dark Eldar use this weapon, the psyker's tormented soul is released and its power has the potential to consume any psyker on the battlefield as their minds are overloaded by the psychic cacophony of anguish.
- Chapter Approved 2003: Feral Orks, pp. 4-10
- Codex: Assassins (2nd Edition), pg. 24
- Codex: Chaos Daemons (4th Edition), pg. 20
- Codex: Craftworld Eldar (3rd Edition)
- Codex: Dark Eldar (5th Edition)
- Codex: Dark Eldar (3rd Edition)
- Codex: Daemonhunters (3rd Edition)
- Codex: Eldar (4th Edition)
- Codex: Eldar (2nd Edition)
- Codex: Imperial Guard (5th Edition), pg. 33
- Codex: Imperial Guard (3rd Edition, 2nd Codex)
- Codex: Imperial Guard (2nd Edition), pg. 78
- Codex Imperialis (1st Edition), by Rick Priestley, pp. 36–37
- Codex: Necrons (3rd Edition)
- Codex: Orks (5th Edition)
- Codex: Orks (4th Edition), pp. 36-37
- Codex: Orks (2nd Edition)
- Codex: Space Marines (6th Edition), pp. 80, 165
- Codex: Space Marines (5th Edition), pp. 56-57
- Codex: Space Marines (4th Edition), pg. 17
- Dark Heresy: Ascension (RPG), pp. 40-41, 124-126, 128-134, 152, 170, 178
- Dark Heresy: Blood of Martyrs (RPG), pp. 10, 17, 21
- Dark Heresy: Core Rulebook (RPG), pp. 74, 158, 160, 246, 248, 251, 273
- Deathwatch: Core Rulebook (RPG), pp. 182-200, 246–264
- 'Ere We Go: Orks in Warhammer 40,000 (1st Edition), pp. 50-55
- Horus Heresy: Collected Visions, pg. 38
- How To Paint Space Marines (Supplement), pg. 46
- Index Astrates - Volume I (Digital Edition)
- Insignium Astartes, pg. 42
- Realm of Chaos: Slaves to Darkness, pg. 213
- Rogue Trader: Core Rulebook (RPG), pp. 48, 154-155, 303, 309
- Rogue Trader: Into the Storm (RPG), pg. 199
- Rogue Trader: The Navis Primer (RPG), pp. 3, 48-63, 104-107, 130, 143
- The Horus Heresy - Book One: Betrayal (Imperial Armour) by Alan Bligh, pg. 21
- Warhammer 40,000: Rogue Trader (1st Edition), pp. 133, 147-148
- Warhammer 40,000 Rulebook (Digital Edition) (7th Edition), pp. 275, 279, 320, 328, 541, 543
- Warhammer 40,000 Rulebook (6th Edition), pp. 138-139, 165, 177, 404, 418-423
- Warhammer 40,000 Rulebook (5th Edition), pp. 104, 124
- Warhammer 40,000 Rulebook (4th Edition), pp. 94, 123
- Waaargh! Da Orkz (1st Edition), pp. 30-31
- White Dwarf 326 (US), "Psykana Librarius - Space Marine Librarians in Warhammer 40,000", pp. 76-89
- White Dwarf 258 (US), "Index Astartes: Psykana Librarius, Space Marine Librarians"
- White Dwarf 227 (US), "Chapter Approved: Dark Angels - Ezekiel, Grand Master of Librarians", pp. 73-80
- White Dwarf 193 (US), "Dark Saviours: Dark Angels Characters - Ezekiel, Grand Master of Librarians, Keeper of the Book of Salvation, Holder of the Keys", pp. 91-95
- White Dwarf 171 (UK), "Dark Millenium: Wargear, Vehicles, and Psykers - Psykers: Adeptus Astra Telepathica Powers," pp. 8-13
- White Dwarf 166 (US), "Space Marines: Codex Imperialis - Librarians", pp. 8-19
- White Dwarf 145 (US), "Renegade: A Five-Part Campaign for Space Crusade - Campaign Background, Librarians", pp. 10-25
- White Dwarf 140 (UK), "Space Fleet," by Jervis Johnson, Andy Jones, Simon Forrest and Rick Priestley, pp. 46-75
- White Dwarf 134 (US), "Ork Warbands in Advanced Space Crusade - Weirdboyz," pp. 66-75
- White Dwarf 124 (US), "`Ere We Go! Preview - Weirdboyz," pp. 46-58
- White Dwarf 123 (US), "Ork Army List: `Ere We Go! Preview," pp. 26-69
- Xenology (Background Book)
- Flight of the Eisenstein (Novel) by James Swallow
- Thousand Sons (Novel) by Graham McNeill
- Prospero Burns (Novel) by Dan Abnett
- Tales of Heresy (Anthology), "The Voice" by James Swallow
- The Outcast Dead (Novel) by Graham McNeill
- Caves of Ice (Novel) by Sandy Mitchell
- Faith and Fire (Novel) by James Swallow
- Heroes of the Space Marines (Anthology), "Headhunted" by Steve Parker
- Eisenhorn (Novel) by Dan Abnett
- Ravenor Rogue (Novel) by Dan Abnett
- Warhammer 40,000: Fire Warrior (Video Game)