Kael'thas Sunstrider was the Prince of Quel'Thalas, the last of the Sunstrider dynasty, as well as a senior member of the Kirin Tor. After the fall of Quel'Thalas, Kael'thas led what remained of his people, the sin'dorei, in the service of the Alliance. Striving to placate his people's addiction to magic, he later covertly allied with Illidan Stormrage, but betrayed him to the Burning Legion when its master, the demon lord Kil'jaeden, enticed Kael with the promise of salvation for the blood elves.
He was branded a traitor after his allegiance to the Legion was revealed, losing the support of Quel'Thalas. Defeated in the Tempest Keep, he would be brought back by his demon masters and return to Azeroth a shadow of his former self. Kael'thas' purpose was to summon Kil'jaeden through the Sunwell, but his plans were foiled by the Shattered Sun Offensive agents and the sacrifice of Anveena Teague. He was defeated by their forces in Magisters' Terrace.