Ku'gath

Ku'gath the Plaguefather is a Great Unclean One who fell into Nurgle's cauldron as a mite and crawled out as a chemist. He wants a plague that even the gods would catch. Until the Plague Wars he sat first in Nurgle's favour, which is a ranking system measured in poxes.

He bottled Guilliman's blood on Parmenio, finished the Godblight, and ignored an order to pull back to the Scourge Stars because Iax looked like a better laboratory. A Cadian tank commander rammed him and put a power sword through his skull. The cauldron shard went with him.

Rotigus found the leftovers in the Warp and explained, cheerfully, that Nurgle was no longer amused. Ku'gath will return. The recipe will be meaner. The favour will not.