- "Those who ignore the blessings of the gods of the Warp are doomed to suffer at their hands."
- — Musim, Advisor to Am-Ord the Merciless
A Sorcerer is the most powerful type of psyker found among the Chaos Space Marines and the other Forces of Chaos, serving the same role as Librarians do for Loyalist Space Marine Chapters and Sanctioned Psykers do for the Imperial Guard, though many powerful Sorcerers can also be considered psychically-gifted Champions of Chaos. Instead of the subtle psychic manipulation and divination used by the Farseers of the Eldar or the strength-boosting powers of the Space Marine Librarians, the Sorcerers of Chaos wield death, destruction, and mutation, the mightiest powers of the Warp.
During the early years of the Great Crusade many Astartes of the Space Marine Legions began to display powerful psychic abilities. One such Legion where psychic powers were particulalrly prevalent was the Thousand Sons. The Astartes of the XV Legion welcomed this development, for they sought to further emulate the Emperor of Mankind. This development was reluctantly tolerated by the Emperor, who was greatly wary of psychic abilities wielded by anyone other than himself or Malcador the Sigillite, though the Thousand Sons' abilities proved to be a powerful weapon for the Imperium during the Great Crusade. At the urging of Magnus the Red and some of his fellow Primarchs, this led to the creation of the Librarius within each Legion, whose psychically gifted Battle-Brothers would seek the betterment of their Legion and the expansion of the burgeoning Imperium of Man.
Throughout many of their campaigns the Thousand Sons made extensive use of Sorcerers, and their Warp-derived powers would leave whole populations in thrall to their will rather than carrying out a planetary conquest through a costly full frontal assault like the other Space Marine Legions. This tactic earned the ire of Leman Russ of the Space Wolves Legion who saw anything less than a frontal assault as dishonourable and cowardly. Over the following decades some of the Primarchs voiced their concern that these so-called "psyker" Astartes were allowed to exist and be a part of the Emperor's Great Crusade. Rumours and condemnations began to spread about the Thousand Sons Legion amongst the other Expeditionary Fleets. The most vocal of these detractors were the Primarchs of the Death Guard, Imperial Fists and Raven Guard Legions.
These tensions finally came to the fore when the Emperor called for the Council of Nikaea, a great Imperial conclave held on the world of Nikaea in the midst of the Great Crusade that was intended to determine whether or not the use of psychic sorcery represented a boon or a grave danger to Mankind and the newborn Imperium of Man. Ultimately, the existence of psykers in the Imperium was allowed but tightly restricted under centralised Imperial control, while the potent and unrestricted use of psychic abilities that was defined as sorcery was officially banned. The Emperor was most displeased by the Thousand Sons' dabblings in manipulating the corrupting powers of the Warp and later forbid the use of sorcery by either Magnus the Red or the members of his Legion. The psychically powerful Primarch Magnus the Red and his Thousand Sons would continue to study such powers in secret on their homeworld of Prospero, ultimately leading to their damnation by Chaos, and the scouring of their world by the Space Wolves, unleashing a deadly rivalry that has lasted unto the present day.
During the Horus Heresy, the Librarians of those Traitor Legions that spat on their oaths of fealty to the Emperor and dedicated themselves to Chaos received new psychic powers. The only exception were the Librarians of the World Eaters, who were hunted down and slain by their brethren as a bloody sacrifice to Khorne, for the Chaos God of war and murder hates all practitioners of sorcery, which he sees as dishonourable trickery when compared to the joys of simple, blood-drenched slaughter.
It is not only the servants of the Ruinous Powers who have been tempted to draw upon sorcery. For those who already tread a fine line between righteous power and damnation like Space Marine Librarians, the temptation to wield the energy of Chaos for selfish means can be overwhelming. It is for this reason that the Emperor once sought to ban the use of all psychic powers, fearing that no human being save himself could be trusted to wield such powers without falling to corruption by the Warp. Although all Librarians are tested for the mental fortitude to withstand daemonic possession and the lures of the Dark Gods, and are constantly monitored by their Chapter, there are those who still succumb.
The line between the basic use of psychic power and what constitutes sorcery is blurred, and every time a Librarian uses his powers he is risking corruption. He may overreach his abilities, unwittingly drawing on more power than he can control, and by these means attract the attention of the Chaos Gods. From that moment, he must endure cold whispers in his dreams, visions of immortality and promises of untold power. There are those who cannot withstand this incessant temptation, and fall to Chaos. These tragic characters are amongst the most iconic archeytpes of Chaos for they have embraced the Ruinous Powers in open defiance of the dictates of the Imperium. Sorcerers of Chaos are vilified and feared, and one of the most hated foes of the Imperial Inquisition, who consider them the most severe of blights upon the galaxy.
Unrestrained by concerns about corruption or morality, a Chaos Sorcerer's powers can be used to destroy through the most flamboyant and pyrotechnic means imaginable. Chaos Sorcerers can hurl bolts of raw Warp energy at the enemy, curse them with Nurgle-spawned plagues and diseases, animate their dead bodies as flesh-eating zombies or physically shape-shift them into a formless blob of flesh. Most Chaos Sorcerers bear the Mark of Tzeentch, who is the Changer of the Ways and the Chaos God of Sorcery, but sometimes Sorcerers bearing the Marks of Nurgle the Plague Lord or Slaanesh, the Prince of Pleasure, also appear. Khorne despises the use of sorcery rather than brute physical power and will specifically obliterate any psyker who would beseech him for power, thus no Sorcerers appear in his service. The Traitor Legion with the most powerful Sorcerers is the Thousand Sons, who are wholly dedicated to the service of the Changer of Ways.
The primary difference between a true Sorcerer and a standard psyker is that the former draws much of his power from dark rituals, daemonic pacts and unholy incantations which all draw to some extent on the power of Chaos. Even a person without any psychic gifts can become a powerful Sorcerer through the use of Warp lore, but this process is fraught with terrible dangers to both body and soul. Such Heretics constantly seek out additional sources of esoteric and forbidden information. They have studied a broad array of arcane knowledge, including xenos practices, legends, and secrets long thought lost. No targets or types of data may be off-limits. While Sorcerers are likely to favour arcane knowledge tied to the dark arts, they realise that the Ruinous Powers may have uses for seemingly mundane bits of data. Virtually any information is useful as it could be enough to persuade their sponsors within the Warp to empower them yet further. The notion of forbidden knowledge is anathema to these Heretics, as they know that their personal destinies transcend any mortal strictures.
An actual psyker can drastically increase his powers by using the dark arts, but at the same time the sorcerous practitioner becomes more vulnerable to the perils of the Warp. Sorcery has been strictly forbidden on many worlds since even before the foundation of the Imperium of Man and the edicts against it made by the Council of Nikaea, but its power still lures thousands of Chaos Cultists to their damnation every year. Even amongst the servants of the Emperor of Mankind, such as Inquisitors of the Radical philosophical persuasion, there are some who believe that sorcery can be used for the betterment of Mankind, as Magnus the Red once did.
Most Sorcerers of Chaos are members of a larger warband of Heretics or Chaos Space Marines. This can lead to conflict within the warband, as the Sorcerer is rarely willing to accept the commands of the Chaos Champion who serves as its leader, unless that leader has the force of will and strength of arms to maintain an iron command. Many warbands have splintered when a Sorcerer of Chaos attempted to take command, leading a portion of the members towards a goal distinct from that of their Chaos Lord. This may even result in the warlord’s death, reminding his fellows of the risk of maintaining such a powerful individual as an advisor.
- Magnus the Red - Magnus the Red is the Daemon Primarch of the Thousand Sons Traitor Legion and is currently an extremely powerful Daemon Prince of the Chaos God Tzeentch. He was also known during the early years of the Imperium as the Crimson King and the Red Cyclops. A giant in both physical and mental terms whilst still an inhabitant of the Materium, the copper-skinned Magnus possessed tremendous innate psychic ability, and constantly sought to understand the nature of the Warp, becoming a Sorcerer of formidable power. Magnus thought he would be able to control the Great Ocean of psychic energy that was the Warp; however, his prodigious and careless application of his psychic gifts eventually caused him to fall out of favour with his father, the Emperor of Mankind, as well as with the majority of his brother Primarchs. His psychic immaturity, recklessness, and arrogance also caused his own undoing, as it eventually brought about his own damnation and servitude to the Dark God of Change, Tzeentch. In the end, Magnus lead his XV Legion to the banner of Horus and fought on the Arch-Heretic's side during the Great Betrayal of the Horus Heresy. He survived those events and ascended to the position of a Daemon Prince of Tzeentch as a reward for his service to the Lord of Change.
- Ahriman - Ahriman is the former Chief Librarian of the Thousand Sons, Captain of its 1st Fellowship and the Magister Templi of its Corvidae Cult. He was banished from the XV Legion by Magnus after casting the Rubric of Ahriman using knowledge derived from the Book of Magnus, which halted the corrupting mutations which plagued the Thousand Sons after their fall to Chaos, but resulted in the creation of the mindless Rubric Marines. During his banishment, Ahriman has continuously sought out knowledge across the galaxy to bring him closer to an understanding of Tzeentch and Chaos itself. His actions have recently healed the breach between him and Magnus the Red that was opened by his casting of the Rubric of Ahriman.
- Karlsen - After his Legion's fall to Chaos following the Scouring of Prospero, Karlsen became a formidable Sorcerer and Chaos Champion of Tzeentch. A veteran of the Long War, Karlsen has fought with the Thousand Sons throughout many of its significant moments in history, including the defence of his homeworld when it was razed by the Space Wolves Legion, the Battle of Terra and countless other campaigns over the last ten millennia. His lifespan has been unnaturally extended by the dark blessings of his patron god. Over the long millennia, Karlsen has gone insane on multiple occasions due to the burden of his cursed, unending existence, though he has been able to perform the blasphemous ritual known as the Dark Communion in order to safely store his memories. As a follower of Tzeentch, he has been "blessed" with several noticeable mutations, which include one of his hands fusing with his archaic Bolter, which he is able to operate with his mind. Another mutation are the unnaturally lengthened, tentacle-like fingers on his opposite hand.
- Jharek Kelmaur - Jharek Kelmaur was a Chaos Sorcerer of the Iron Warriors Traitor Legion who served the Chaos Lord known only as "The Warsmith" during the siege of the Imperial Fortress World of Hydra Cordatus. Kelmaur aided the Warsmith in obtaining the hidden stores of Imperial Fists gene-seed kept there. The Imperial Fists had always been the most hated foes of the Iron Warriors since the days of the Horus Heresy but the Iron Warriors needed fresh Astartes gene-seed to grow their numbers since the power of Chaos tended to mutate their own gene-seed to the point that it was unsuitable to create new Chaos Space Marines. The Iron Warriors Sorcerer served as an advisor on all matters psychic and would often receive and interpret visions by communing with the Ruinous Powers. During the siege of the large Imperial citadel and manufactorum complex on Hydra Cordatus known as the Tor Christo, Kelmaur neglected to inform the Warsmith of a faint psychic beacon that had managed to be sent from the surface of the planet. Keeping this information to himself, the sorcerer thought it best if he handled the manner personally. Kelmaur attempted to send the Iron Warriors flagship Stonebreaker to the system's warp translation point in order to intercept any Imperial reinforcements. This action would prove dire to the scheming Kelmaur, who in his arrogance, allowed an Imperial Fists company to slip past the Stonebreaker and infiltrate to the planet's surface and reinforce the besieged garrison. For his duplicity and arrogance, the Warsmith transformed Kelmaur into a Chaos Spawn after he had served his purpose.
- Madox - Madox was a notable Chaos Sorcerer of the Thousand Sons who led several plots to destroy his Legion's ancient foes, the Space Wolves Chapter. He reserved a special hatred for the Wolf Lord Ragnar Blackmane, who foiled several of his plots when they confronted one another across several decades of the late 41st Millennium. It is presumed that he was finally killed on the world of Charys, where Madox hoped to enact a Chaotic ritual to fully corrupt the gene-seed of the Space Wolves and set them on the path of damnation. The ritual used to enact the Chaos Sorcerer's blasphemous ritual was interrupted by the timely intervention of Ragnar Blackmane and his fellow Space Wolves. During their final confrontation, Blackmane managed to wrest the Spear of Russ from Madox and used that sacred artefact of his Chapter to impale Madox through the faceplate of his armour, apparently killing him. Many decades later, while suppressing a Chaos rebellion on an unnamed world, Ragnar Blackmane heard rumours that the Sorcerer Madox was still alive and leading the Forces of Chaos. Though unsure if the rumours were true, it could be likely that Madox had indeed been resurrected through malefic means, as he has done so in the past by using the body of a Chaos Cultist. If this is indeed true, then Madox eventually could return once more to the material realm by the will of the Dark Gods.
- Mordeghai - High Magister Mordeghai, a gifted Chaos Sorcerer, was a Tribune Senioris to Magnus the Red at the Siege of the Imperial Palace during the Battle of Terra. Sometime during the 41st Millennium, Mordeghai had foreseen that if his Death Guard arch-rival Festardius gained control of the world of Mekenna VII, the Plague Lord would use his new influence to turn Mortarion's forces against Mordeghai's cabal. The best way to prevent this from happening was to wrest control of the world from Festardius once the Warmaster Davroth had departed. Mordeghai believed he had more than enough Thousand Sons Rubric Marines to accomplish this.
- Necrosius - Necrosius was once an Apothecary of the Death Guard Legion during the Great Crusade whose original name has long been purged from all Imperial records. During the early days of the Horus Heresy, soon after the Death Guard turned against the Emperor of Mankind, when the Traitor Legion's fleet was becalmed in the Warp on the way to Terra and assaulted by the infectious corruption of Nurgle, the man who would become Necrosius the Undying and his fellow Apothecaries among the Astartes of the Death Guard turned their every art and skill against the strange plagues sweeping their ranks. But it was all to no avail. When Necrosius heard the voice of his new lord chortling and whispering to him in the murmerous wings of carrion flies and the sibilant gurgling of rotted, decaying organs, he fully accepted the nightmare truth of what he and his fellows had become, and embraced the service of his vile God. Necrosius became a true convert to Nurgle's cause, casting aside his past learning and cherished role as a healer of his Battle-Brothers. He now chose to give himself, blighted soul and rotted body, to the lore of death and the pursuit of daemonic sorcery, and soon excelled as a master of the dark arts of necromancy. Now this bitter and twisted Chaos Sorcerer is Nurgle's sworn servant and the master of the warband of Chaos Space Marines known as the Apostles of Contagion.His dark arts of necromancy can awaken the dead to a nightmarish half-life, unleashing the Zombie Plague of the Plague Lord upon friend and foe alike.
- Nihilan - Nihilan was a former Salamanders Librarian who turned Renegade and joined the warband of the Black Dragons Renegade Chaplain Ushorak. The Salamanders responded rapidly, sending a strike force composed of the 3rd Company and led by Captain Ko'tan Kadai which made their way to the Cemetery World of Moribar. While Ushorak delved into the secret crypts beneath the sepulchre world, the Salamanders and the Renegade followers of Ushorak fought savagely through the crematoria of that ash-blanketed world. At the height of the fighting, Ushorak was plunged into the central furnaces at the heart of the planet, and Nihilan tried to save the Chaplain but failed and was horribly burned in the process, barely surviving at all. From the tattered remnants of Ushorak's followers the newly christened Chaos Sorcerer Nihilan forged the Dragon Warriors Chaos Space Marines warband, determined to exact vengeance on the Salamanders and the people of Nocturne.
- Atum Sum - A Chaos Sorcerer of prodigious ability, Atum Sum is known to the Inquisition as an acolyte of Ahriman, Chief Librarian of the Thousand Sons Traitor Legion. He is steeped in the power of the Warp, and a known master of the daemonic. It is said that the daemonic servants of Tzeentch attend him as lesser men command the loyalty of stooping servants, though the veracity of this claim seems unlikely to those versed in the ways of the God of Change. Furthermore, he appears to have an uncanny mastery of the ebb and flow of possibility, manipulating the shifting tides of the Warp to appear at any time and place he desires. It is doubtless true that Atum Sum is a dire threat to the Imperium, for his appearance is often seen to precipitate daemonic incursions of the most destructive kind. Needless to say, Atum Sum’s appearance in the Jericho Reach is a cause for dread, and several groups within the Inquisition have already set in motion plans to discern his purpose and if possible, oppose it. To date, Atum Sum has been encountered in the warzones surrounding the Hadex Anomaly, leading some to suspect that he is involved in some grand scheme to utilise the weird Warp energies streaming from it. Some have even claimed that Atum Sum has conversed with the Anomaly, or with some vast, unknowable intelligence deep inside and beyond it. Whatever the truth, several Inquisitor Lords of the Ordo Chronos were known to be mustering a coalition to stymie his plans when they disappeared, suggesting that his powers are an order of magnitude greater than any had dared to believe.
- Blight-Master Ussax - Ussax is a Veteran of the Death Guard Traitor Legion, and known as a member of the inner circle of Chaos Sorcerers that serve the Daemon Primarch Mortarion. He is well known to the Ordo Malleus and to the Grey Knights, and has been responsible for countless millions of deaths throughout the millennia. Ussax is held to be one of the most darkly gifted concoctors of blights, afflictions and plagues serving the Death Guard, and his recent appearance in the warzones of the Jericho Reach, attended by a cadre of Plague Marines, is a cause for much concern amongst those with knowledge of his capabilities. According to recent findings presented to the Chamber of Vigilance of Watch Fortress Erioch, Blight-Master Ussax has been present in the Reach for around three standard years, travelling from one warzone to the next. At each battlefield, he gathers up a grim and unspeakable harvest from the dead and the dying, before returning to some as yet undiscovered fastness to concoct his latest ague. This he then unleashes upon the next battlefield he attends, once more harvesting the bodies of the victims. It is feared that the Blight-Master is refining his plagues, using the raging conflicts of the Jericho Reach as some vile breeding ground for new agonies to unleash upon an unsuspecting galaxy in Father Nurgle's name.
- Amadeus Volkstein - Volkstein was once a Loyalist Librarian Epistolary known as Vanneus before being corrupted by the promise of knowledge and power offered by Tzeentch, and now leads the Renegade Chaos Space Marine warband known as the Oracles of Change.
- Ygethmor - Ygethmor is a formidable Sorcerer Lord of the Black Legion and serves as Abaddon's close advisor and current Lord Deceiver, a powerful Chaos Sorcerer whose visions of the Warp lead the Black Crusade from star system to star system.
- Zaraphiston - Zaraphiston once served as Abaddon's foremost Sorcerer Lord and close advisor during Abaddon's 12th Black Crusade, better known as the Gothic War. Zaraphiston served as Abaddon's former Lord Deceiver, helping to guide the Warmaster of Chaos during the Black Crusade through his prescient visions from the Warp.
- Apocalypse, p. 171
- Black Crusade: Core Rule Book (RPG), pp. 60-61
- Codex: Chaos Space Marines (4th Edition)
- Codex: Chaos Space Marines (3rd Edition, 2nd Codex)
- Codex: Chaos Space Marines (3rd Edition, 1st Codex)
- Codex: Chaos (2nd Edition), pp. 17, 46
- Dark Heresy: Disciples of the Dark Gods (RPG), pp. 116-119
- Deathwatch: First Founding (RPG), pp. 85, 88
- Imperial Armour Volume Seven - The Siege of Vraks - Part Three, pp. 14-15, 143
- Index Astartes I, "Psykana Librarius - Space Marine Librarians"
- Index Astartes III, "Masters of Forbidden Knowledge - The Thousand Sons Space Marine Legion", pp. 62-69
- Index Astartes IV
- Realm of Chaos: Slaves to Darkness (1988), p. 243
- The Fall of Medusa V (Booklet), p.12, 16-17
- Warhammer 40,000: Wargear (2nd Edition), "Dark Communion" by Bill King, pp. 78-80
- White Dwarf 326 (US), "Psykana Librarius", p. 76
- White Dwarf 287 (UK), "Death by a Thousand Cuts," p.36
- White Dwarf 286 (UK), "The End Is Night," p. 71
- White Dwarf 267 (US), "Index Astartes First Founding: Masters of Forbidden Knowledge, The Thousand Sons Space Marine Legion"
- White Dwarf 263 (US), "Runes of Forging - Aaron Dill's Crazy Conversion Competition Finale: Magnus the Red, Demon Lord of Tzeentch", pp. 28-29
- White Dwarf 258 (UK), "Psykana Librarius: Space Marine Librarians"
- White Dwarf 238 (US), "The Slayer of Worlds: History of the Origins and Activities of the Planet Killer" by Gavin Thorpe, pp. 103-109
- White Dwarf 230 (US), "Bitter and Twisted: Ahriman" and "Chapter Approved: Thousand Sons Terminators", pp. 39-43, 71-79
- White Dwarf 227 (US), "Chapter Approved - Ahriman: Chaos Sorcerer, pp. 73-80
- White Dwarf 202 (US), "The Sorcerer: Tzeentch, Ahriman", pp. 9-14
- White Dwarf 199 (US), "Chaos: The Long War"
- White Dwarf 150 (US), "'Eavy Metal: Epic Daemons - Magnus the Red: Primarch of Tzeentch", pp. 68-69
- Horus Heresy Novel Series:
- False Gods (Novel) by Graham McNeill
- A Thousand Sons (Novel) by Graham McNeill
- The First Heretic (Novel) by Aaron Dembski-Bowden
- Prospero Burns (Novel) by Dan Abnett
- Aurelian (Novella) by Aaron Dembski-Bowden
- The Outcast Dead (Novel) by Graham McNeill
- Age of Darkness (Anthology), "Rebirth" by Chris Wraight
- Atlas Infernal (Novel) by Rob Sanders
- Battle of the Fang (Novel) by Chris Wraight
- Blood Ravens: Dawn of War Omnibus (Novel compilation) by C.S. Goto
- Tome of Fire Trilogy:
- Salamander (Novel) by Nick Kyme
- Firedrake (Novel) by Nick Kyme
- Nocturne (Novel) by Nick Kyme
- The Space Wolf Omnibus (Novel) by William King
- Space Wolf: The Second Omnibus (Novel) by William King and Lee Lightner
- Storm of Iron (Novel) by Graham McNeill
- Ahriman: Exile (Novel) by John French