The Rift Stalkers is a Loyalist Space Marine Chapter comprised entirely of Primaris Space Marines, created from the rare lineage of the Raven Guard and raised during the Ultima Founding of 999.M41. These supreme transhuman warriors were created by order of Roboute Guilliman, the recently resurrected Primarch of the Ultramarines, who had tasked Archmagos Dominus Belisarius Cawl with crafting a legion of new transhuman warriors to serve as Humanity's last line of defence following the Horus Heresy. Even then, Guilliman foresaw a time of encroaching darkness when Chaos would threaten the galaxy itself. These gene-crafted warriors are intended to protect the Imperium of Man against the gathering darkness from Chaos, xenos and the myriad threats that threaten the Imperium on all sides. They are the key components of the resurrected Primarch's Indomitus Crusade to reclaim the galaxy for Mankind.
The Rift Stalkers is a fleet-based Chapter, and its task is to patrol the Cicatrix Maledictum, as many foul abominations emerge out of that great rent in reality. In addition to slaying the Emperor's enemies, the Rift Stalkers diligently seek a method of reconnecting with the hundreds of thousands of worlds cut off in the galactic north of the Imperium Nihilus.
For ten millennia, Archmagos Dominus Belisarius Cawl has been working on a task set for him by the Primarch Roboute Guilliman before he was mortally wounded by the Daemon Primarch Fulgrim in the days after the Horus Heresy: a new legion of transhuman warriors. Developed on orders from Guilliman 100 standard centuries past, Primaris Space Marines were diligently developed and perfected by the Priesthood of Mars during the long intervening millennia. As an optimist, but never a fool, Guilliman learned from the mistakes of the Horus Heresy, and he foresaw that the Forces of Chaos would never relent in their aim to bring the Imperium low. He anticipated that devastating times would once again engulf the galaxy and knew that warriors resilient enough to stand against them would be needed as never before. That time has surely come. Now, as the Imperium of Man is poised on the brink of annihilation at the hands of Chaos, his task is at last complete.
The Primaris Space Marine is a new breed of hero for this, the darkest age in the Imperium's history. These new warriors are the next step in the evolution of the Emperor's Angels of Death -- genetically altered from their brethren to be bigger, stronger and faster -- timely reinforcements for the Imperium's armies as their enemies close in for the kill in the wake of Abaddon the Despoiler's 13th Black Crusade and the birth of the Great Rift dividing the Imperium in two.
To aid them in battle, these gene-forged warriors are equipped with new arms and armour forged on Mars itself, such as the Mark X Tacticus Pattern Power Armour worn by the Primaris Space Marine Intercessors, which combines the most effective elements of ancestral Horus Heresy patterns of battle-plate with more recent developments in Power Armour technology; the Mark II Cawl Pattern Bolter, the archetypal firearm of the Adeptus Astartes, now re-engineered, re-crafted and perfected, and Redemptor Dreadnoughts.
At the dawn of the Indomitus Crusade to retake the Imperium from the advancing armies of Chaos and xenos alike, Lord Commander of the Imperium Roboute Guilliman has gathered his new armada, along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood and a vast war host of Primaris Space Marines as he fights to liberate the scattered bastions of the Imperium. Some, Guilliman has forged into new Space Marine Chapters, whole brotherhoods comprised only of these new transhuman warriors. Others he has offered to the existing Space Marine Chapters. Many Chapter Masters have welcomed their Primaris brethren into their ranks, accepting the new reinforcements gladly. Others, though, view these new creations with suspicion or outright hostility, claiming that the Emperor's work should never have been meddled with by mere mortals.
Though they are a step removed from their brothers, the Primaris Space Marines still bear the gene-seed of their Primarchs, and some dissenting voices worry how this new type of warrior will react with the known genetic quirks and flaws of some of the more unusual Chapters, such as the Blood Angels and the Space Wolves. Though the Primaris Space Marines offer new hope to a besieged Imperium, the future remains a dark and uncertain place...
The Rift Stalkers wear white Mark X Tacticus Pattern Power Armour, the polar opposite of their progenitors who prefer midnight black. The Aquila or Imperialis on the chest is black. The black squad specialty marking on the right shoulder pauldron (Tactical, Assault, Devastator or Veteran) designates squad specialty. The colour of the trim on the right shoulder pauldron indicates company number in accordance with the tenets of the Codex Astartes. The left shoulder pauldron proudly displays the Chapter's iconography -- the same black raven heraldry of the Raven Guard. A black Low Gothic numeral stenciled on the left poleyn (knee guard) indicates squad number.
The Rift Stalkers' Chapter badge is the same stylised black raven centred on a field of white utilised by their parent Chapter.
- Codex Adeptus Astartes - Space Marines (8th Edition), pg. 53