Kel'thuzad

Kel'thuzad was once an Archmagi and member of the Council of Six in Dalaran, but was exiled for practicing necromancy---later becoming servant of the Lich King and leader of the Cult of the Damned.

Legacy
Given that Kel'thuzad was the Archlich of the Scourge, many had taken up his teachings and modeled themselves after him. One such group was the Thuzadari, a sect of Shadowmagi and Necromancers within the defiled city of Stratholme.