The Corpus Brethren is a warband of Chaos Space Marines dedicated to the Pleasure God Slaanesh. They were once a Loyalist Chapter of Space Marines of unknown origin and Founding known as the Sentinels. They were corrupted after entering the Eye of Terror in 321.M37 as part of the Imperial Abyssal Crusade. During their sojourn into the Eye, the Sentinels found signs of Chaos Space Marine infestation and made planetfall on the Daemon World of Oliensis, which was shaped like a morbidly-obese man. The Sentinels hunted down and exterminated the goat-headed hedonists that frolicked there, but the cacophony of battle stirred Slaaneshi Noise Marines, who came pouring out from the planet's fleshy pores and soon battle was joined. The raging conflict stirred the living planet itself, which awoke and swallowed the combatants into a large chasm. By the time they reemerged the Sentinels were no longer recognisable, having been transformed into the cannibalistic Corpus Brethren.
The Corpus Brethren were a formerly Loyalist Chapter known as the Sentinels. Following the Ecclesiarchal Purges of 321.M37, a dozen star systems were engulfed by Warp Storm Dionys, its echoes rippling along the spiral arms of the galaxy as it raged through the Empyrean. Records of mutation and Chaos Cultist activity quadrupled overnight. Worse yet, it was not only the citizens who were affected by the sudden influx of Chaos. Many of the Space Marine Chapters with homeworlds affected by the Warp Storm found that the secret imperfections in their gene-seed were writ large upon their new recruits, giving rise to a wave of disturbing manifestations both physical and psychological. The Sentinels Chapter were one such Loyalist Chapter of Astartes that had been affected by these Warp Storms.
When the Ecclesiarchy heard of this sinister tum of events, Saint Basillius the Elder demanded that all those Chapters of the Adeptus Astartes whose homeworlds had been touched by the Warp Storm be rendered unto his judgement. Such was the elder's influence with the High Lords of Terra that within a standard year this had come to pass. After a series of stringent tests and prognostications, hundreds of Chapters were deemed unaffected by the Warp Storm. No less than thirty were found wanting. The Judged, as these fallen Chapters came to be known, volunteered for a redemptive Penitent Crusade. The most militant of their number demanded the right to purify their tainted flesh in the fires of battle, to make a noble end from tragic misfortune. To the surprise of his closest advisors, Saint Basillius agreed to this proposal. He saw it fitting to send the accused into the Eye of Terror, taking the fight for the Imperium's future to the Daemon Worlds inhabited by the Traitor Marines.
A representative from each of the doomed Chapters held an emergency Council of Dismay to discuss the proposed Crusade. After scant hours of debate, they acquiesced to Basillius' demands, for they believed that martyrdom was preferable to an existence of suspicion and doubt. The last few days of 321.M37 saw a solemn procession of Strike Cruisers and Battle Barges pass through the Cadian Gate into the Eye of Terror, relay systems dormant and heraldic colours obscured by black mag-plates. One by one, the Chapters of The Judged disappeared into the iridescent dust nebulae that surrounded the Eye. As the massive Space Marine flotilla entered the Eye of Terror, they were set upon by a massive Chaos warfleet. The resultant battle was so fierce that the ships of The Judged were forced to retreat and were scattered to the furthest corners of the Eye.
The ever-vigilant Astartes of the Sentinels Chapter quickly found signs of Chaos Space Marine infestation, making planetfall upon the fleshy crust of Oliensis. Only when their long-range scans of a nearby mountain range revealed the topography of a human face did they realise the Daemon World they had invaded took the form of a morbidly obese man curled into a foetal ball. Putting their doubts to one side, the Battle-Brothers of the Sentinels hunted down and exterminated the goat-headed mutant hedonists who frolicked between the tree-trunk hairs soaring up into the fiery skies above. The ecstatic death-bleats of the Chaos Cultists did not go unheard. From the planet's yawning pores came gaudily painted Slaaneshi Noise Marines, their sonic weapons splitting the night air with blood-curdling salvos. The Sentinels crashed headlong into battle with their outlandish foes, but as more and more flesh-worshippers emerged to join the fray, the planet itself stirred, awoken by the din of combat. Lake-sized eyes gleaming, Oliensis shovelled the combatants into its waterfall gullet with a hand the size of a tectonic plate. By the time the Sentinels were regurgitated back into reality, they were unrecognisable as Adeptus Astartes. They had been refashioned into the cannibalistic Corpus Brethren Renegades, every bit as deranged as the Slaanesh-worshipping Heretics they now fought beside.
The Corpus Brethren's warband colours are dirty white with brass trim.
The Corpus Brethren's warband badge is a red, horned daemon head with multiple eyes centred on a field of white.
- Codex Heretic Astartes - Chaos Space Marines (8th Edition), pg. 53
- Codex: Chaos Space Marines (6th Edition), pg. 18