Betrayer... In truth, it was I who was betrayed. Still, I am hunted. Still, I am hated. Now, my blind eyes see what others cannot: that sometimes the hand of fate must be forced! Now go forth... unleash the tides of Doom... Upon all those...who would oppose us."
-Illidan Stormrage, Warcraft 3: The Frozen Throne Leader of the Demon Hunters, Lord of Outland, Betrayer.
Illidan Stormrage is a night elf born Demon Hunter and the founder of the Illidari. He was the former self-proclaimed Lord of Outland, ruling from the Black Temple until his defeat. While being born one of the Kaldorei, as stated by Maiev Shadowsong, he became "neither night elf nor demon, but something more". He is the twin brother of Malfurion Stormrage and was in love with Tyrande Whisperwind. Once an unusually gifted sorcerer, the extent of his powers became difficult to classify due to his powers increasing in large bursts as a Demon Hunter and his having absorbed the powers of the dangerous fel object known as the Skull of Gul'dan.
His pursuit of power and arcane mastery led him to commit a number of horrific acts against his own people and the races of Azeroth, including defecting to Sargeras during the War of the Ancients and creating the second Well of Eternity. For his actions, he was imprisoned for ten thousand years, until his release during the Third War. He came to be called the Betrayer for his acts against the night elf people and carried the title of Lord of Outland. Seeking to bring down her erstwhile prisoner, Maiev allied with Akama to invade the Black Temple, where she cornered Illidan in his inner sanctum and struck him down, bringing an end to one of the most tragic stories in Azeroth's history.
However, Illidan's motivations were revealed to be more complex than previously realized - as he only had the salvation of Azeroth from the Burning Legion in mind. To this end, after his body was stolen by the Gul'dan from an alternative timeline - the prime naaru Xe'ra put events in motion that would eventually lead to the revival of Illidan - of whom she considered the "child of Light and Shadow", and the only one who could stop the Legion.
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Illidan is owned by Blizzard, but he deserved MUCH better than eternity Buttfucking Sargeras with his Warglaives.