Krell

Krell, the Lord of Undeath, was a mighty Chaos Champion in the days before the birth of Sigmar, the ruler of a barbarian tribe that had been corrupted by the Chaos God Khorne. Krell carved out an empire amongst the barbarian tribes of the north and then turned against the Dwarfs to the south. He allied with the Night Goblins that stormed the Dwarf strongholds of Karak Ungor and Karak Varn, and his name is recorded many times in the Great Book of Grudges, though he was eventually slain by the Dwarf hero, Grimbul Ironhelm, during the assault on Karak Kadrin.

Krell's followers carried away his body and buried it in a barrow tomb. Nearly 1,500 years later, Nagash came upon the tomb when he was searching for the Crown of Sorcery. Easily translating the runic inscriptions on the tomb walls, Nagash realised that this barrow held the remains of a mighty champion. Nagash was much pleased, and instantly set about raising this prized hero to fight in his armies.

Krell was placed in command of one of Nagash's Undead legions when he fought against Sigmar at the Battle of the River Reik. Leading from the front, Krell's forces attacked the Empire's Dwarf allies. The battle raged furiously, the Dwarfs stubbornly refusing to give ground against the endless ranks of Undead troops. Just as it seemed the Dwarf line would crumble, Sigmar cut down Nagash. In moments, the Undead army was all but destroyed as units withered and turned to dust. Only Krell and his Grave Guard survived Nagash's defeat. At the head of his troops, he was able to battle his way through the Dwarf lines and escape. Sigmar's forces were exhausted and did not pursue Krell immediately. This proved a costly mistake. Marching night and day, Krell led what remained of his forces on a dance of destruction that cut a bloody swathe across the lands. Entire communities were destroyed, towns sacked, and castles burnt to the ground. To this day, stories of Krell and his Doomed Legion are told across the Empire.

Krell was finally cornered by Sigmar and defeated at the Battle of Glacier Lake, and his body was imprisoned in a magically constructed tomb. Centuries later, Heinrich Kemmler, the Lichemaster, came upon the tomb of Krell and freed the ancient Wight. Kemmler believes Krell to be in his thrall, but the servants of Nagash are not so easily enslaved...

Source

 * Warhammer Armies: Vampire Counts (8th Edition) -- pg. 59