Illidan Stormrage is currently the self-proclaimed Lord of Outland, ruling from the Black Temple. He was born a night elf, and as stated by Maiev Shadowsong, is now "neither demon nor night elf, but something more". He is the twin brother of Malfurion Stormrage and was (perhaps still is) in love with Tyrande Whisperwind. Once an unusually gifted sorcerer, the extent of his powers today are difficult to classify, due to his powers increasing in large bursts as a demon hunter, sorcerer, and having absorbed the powers of the Skull of Gul'dan.
Once we get to the peak of black temple, Illidan will be there, and we will kill him.