When the Burning Legion’s lieutenant, Kil’Jaeden, discovered that his creation the Lich King was becoming too powerful to control, the demon approached the Betrayer, Illidan Stormrage, and offered him great power in return for destroying the Lich King. Using an artifact called the Eye of Sargeras, Illidan succeeded in cracking the glacial ice that kept the Lich King imprisoned, though he failed to destroy him due to the interference of Maiev Shadowsong. With his Frozen Throne broken, the Lich King’s power began to wane and many of the stronger-minded Undead regained their free will. Chief amongst them was the former High Elf Ranger General Sylvanas Windrunner. In control of her own mind and once again possessing corporeal form, Sylvanas set about to free as many free-willed Undead that she could and eventually enslaved the Dreadlord Varimathras as well. Naming her new army the Forsaken, Sylvanas claimed the ruined capital of Lordearon as her own and has turned the royal crypts beneath the crumbling castle into a bastion of Undeath called the Undercity. The Forsaken refer to Sylvanas as The Dark Lady and loyally obey her every command.

Sylvanas’s army consisted only of Banshees and Ghouls before she enslaved Varimathras. Because the lack of brute force initially commanded by her legion, Sylvanas had her Banshees bolster their forces with whomever they could recruit, be they ogres, trolls, murlocs, gnolls, or bandits.