Krell

Krell was a chaos lord of a large tribe of chaos warriors dedicated to Khorne, living roughly 1500 years before the foundation of the Empire. He created a large kingdom somewhere in the future Empire and/or in the chaos wastes. After warring against human barbarians, he turned his attention to the realms of the Dwarfs, allying with Night Goblins. He attacked(and presumably conquered) the Dwarven fortresses of Karak Ungor and Karak Varn, but was defeated and slain while attempting to attack Karak Kadrin by an army led by Grimbul Ironhelm. He was buried on the edge of the chaos wastes, and was re-discovered by Nagash while he was looking for his lost crown of sorcery. Knowing of his skills as a commander and warrior, he decided to resurrect Krell to serve him. He fought in the battle of the river reik, which he presumably survived, as whem Nagash rose himself from the dead again, Krell was ready to serve him.

Sources

-Games workshop website[1]