Lich · Archlich of the Scourge · Scourge · Northrend / Naxxramas
A Kirin Tor archmage who left the order voluntarily to serve The Lich King. He founded the Cult of the Damned, engineered the plague of undeath that destroyed Lordaeron, and was killed and then raised as a lich using the defiled Sunwell.
He summoned Archimonde to Azeroth.
