The Rotworm Brotherhood is a splinter warband of Plague Marines that has become independent of the Death Guard Traitor Legion's central command. This warband is led by a conclave of Death Guard Sorcerers who rebelled against Mortarion. They raise cults of mortal worshippers across the Imperium, their task to multiply like bacilli and spread the worship of Nurgle, undermining civilisation before the Rotworm Brotherhood descends to despoil all.
The Rotworm Brotherhood's Power Armour is the same as that of the Death Guard, composed of decayed and cracked plates of ceramite in light grey with dark green trim. The Rotworm Brotherhood's Chaos Space Marines, like those of the Death Guard, often wear grotesquely warped suits of antique Mark III Iron Power Armour.
- Codex Heretic Astartes - Death Guard (8th Edition), pp. 17