Kael'thas Sunstrider

From wow.incgamers.com

Prince Kael'thas Sunstrider was enslaved, along with his brethren, he then made allies with Illidan Stormrage, and Lady Vashj, the leader of the Naga. Obsessed by the need for magic power, he has abandoned his fellow Blood elves and tried harvesting massive amounts of magic in Outland. Being thwarted by Alliance and Horde heroes, he returned back to Sunwell Isle to bring Kil'jaeden into Azeroth.

He can currently be found in the instance Magister's Terrace.