Illidan: Silence The World - Complete Lore (Warcraft 3 to Legion)

“There is no sacrifice too great if it brings an end to the Burning Legion.”

— Illidan Stormrage[12]
Illidan Stormrage, commonly known as the Betrayer, is the first of the demon hunters, the former self-proclaimed Lord of Outland, the former ruler of the Black Temple, and the original leader of the Illidari. He is the twin brother of Malfurion Stormrage and was, like his sibling, in love with Tyrande Whisperwind. Originally a powerful night elf sorcerer, Illidan officially betrayed his people by defecting to the demonic Burning Legion during the War of the Ancients, though his reasons for doing so were noble as he secretly aimed to repel the Legion's invasion.[13] He eventually returned to the side of his fellow night elves, but his creation of a second Well of Eternity at the end of the war caused his people to name him "Betrayer" and imprison him in the Barrow Deeps below Mount Hyjal. There he remained for over 10,000 years, watched over by the warden Maiev Shadowsong and her Watchers.

When the Legion invaded Azeroth once more during the Third War, Tyrande freed Illidan from his prison in order to have him battle the demons once more. He subsequently consumed the fel energies of the Skull of Gul'dan and transformed into a demon in order to defeat the dreadlord Tichondrius, an act for which he was banished by Malfurion. After the Legion's defeat at the end of the war, Illidan decided to feign allegiance to the demon lord Kil'jaeden by agreeing to destroy Kil'jaeden's traitorous creation, the Lich King, as a way to learn more about his true foe: the Burning Legion.[14] Although he amassed an army of servants in the form of the naga led by Lady Vashj, Illidan's efforts were stopped by the night elves and he was forced to flee to the shattered realm of Outland. There he and his naga gathered new allies in the form of the blood elves led by Kael'thas Sunstrider and the Broken draenei led by Akama, and with their aid he overthrew Outland's tyrannical ruler Magtheridon to claim the broken realm for his own. Illidan later traveled with his allies to the Lich King's stronghold of Icecrown for one last attempt to complete Kil'jaeden's mission, but he was eventually thwarted and nearly killed by the Lich King's champion, the death knight Arthas Menethil.

Returning to Outland, Illidan dropped all pretense of serving Kil'jaeden and mustered his army—the Illidari—to begin his true war against the Burning Legion.[15] He trained an army of elven demon hunters in his own image and began preparing to destroy the Legion world of Argus, but his extreme methods and single-minded focus on his goal led to the alienation of his allies Kael'thas and Akama. Through the manipulations of Kil'jaeden, the Alliance and Horde invaded Outland and began dismantling Illidan's forces in the belief that he was no better than the demons he claimed to fight. Despite succeeding in destroying the demon stronghold of Nathreza, the Betrayer was ultimately cornered and struck down within his own sanctum by Akama, a group of Azerothian adventurers, and his vengeful former jailer, Maiev. Maiev subsequently brought Illidan's corpse to the Vault of the Wardens so that his spirit could suffer the rest of his eternal sentence. There it remained for years until the Legion invaded once more.

A struggle for Illidan's soul ensued between the Legion and the forces of Azeroth, including the remaining Illidari, culminating in Illidan's resurrection atop the Nighthold. The Betrayer subsequently joined forces with Azeroth's defenders as they battled the Legion across the Broken Shore and within the Tomb of Sargeras. During a battle with Kil'jaeden in the Twisting Nether, Illidan used an artifact known as the Sargerite Keystone to open a rift that brought the worlds of Azeroth and Argus together. Illidan accompanied Azeroth's champions as they traveled to Argus to battle the Legion alongside the Army of the Light, whose leader—the prime naaru Xe'ra—believed that Illidan was the Chosen One,[16] a hero of the Light prophesied to end the age of demons.[17] Illidan rejected the idea of having his destiny forged for him and killed Xe'ra when the naaru tried to forcibly infuse him with the Light.[16] The Army of the Light and their allies eventually assaulted Sargeras' seat of power, Antorus, and freed the captive spirits of the titan Pantheon, who imprisoned Sargeras at the Seat of the Pantheon for his transgressions. While the rest of Azeroth's heroes returned home to their world, Illidan chose to remain behind, becoming Sargeras' jailor.