The Bleak Brotherhood is a warband of Chaos Space Marines whose origins remain unknown although they may possibly be a splinter warband of the Warp Ghosts. The Chaos God to whom they offer their allegiance, if any, is unknown.
- Magdelon Incursion (712.M41) - The renegade Bleak Brotherhood makes a compact with a daemonic power for aid in coming wars, the price the entity demands being the casting down of the Crystal City of Magdelon. The renegades enact their pact of the fell bargain, and in so doing attract the attention of the Space Wolves Space Marine Chapter. Wolf Lord Ragnar Blackmane leads his Great Company against the splinter warband, and in the ensuing battle amidst the shattered ruins of the Crystal City the ferocity of the battle is so pleasing to the denizens of the Warp that a major daemonic incursion is triggered. The Space Wolves emerge triumphant, despite the odds. Having been ejected from Magdelon, the Bleak Brotherhood flees to Lycanthos Secundus.
- Lycanthos Drift Campaign (780.M41) - Having been ejected from Magdelon, the Bleak Brotherhood flees to Lycanthos Secundus, where they occupy the mighty bastion known as the Widowmaker. Throughout the Lycanthos Drift Campaign of the Fourth Quadrant Rebellion, this stronghold withstands repeated assaults by numerous Imperial forces for three decades before at last falling to Lufgt Huron and his Astral Claws Chapter in 780.M41.
- 13th Black Crusade (999.M41) - During Abaddon the Despoiler's 13th Black Crusade, the Bleak Brotherhood was one of the Chaos Space Marine warbands that participated in the massive assault by the Forces of Chaos against the Cadian Gate.
The Bleak Brotherhood wears jet-black coloured Power Armour with green flames.
The badge of the Bleak Brotherhood is a green outline of a locust's head on a black background.
The Bleak Brotherhood possesses the same badge and colours as the Chaos Space Marine warband called the Apocalypse Company. It is unknown whether this is meant to signal that both warbands possess a prior relationship or whether it was just a mistake on the part of Games Workshop.
- Codex: Chaos Space Marines (4th Edition), pg. 18
- Imperial Armour Volume Two, Second Edition - War Machines of the Adeptus Astartes, pg. 20
- Imperial Armour Volume Nine - The Badab War, Part One, pg. 59
- Imperial Armour Volume Thirteen - War Machines of the Lost & The Damned, pg. 24