Flavus was the human king of Naabridum. He ruled Naabridum for decennia before the peace was disturbed. He was killed in The Cataclysm, but was resurrected by a Necromancer. In life, he was an strong and impressive man. This traits carried over to his undead form. His resurrection left him with magic abilities.
After The Cataclysm he remained king of the other undeath from Naabridum. Under his command, the undead of Naabridum marched out of their kingdom to flee from the evil. They entered the neighboring kingdom of Efentêam and took shelter in the Steel Cavern.