The last of the Sunstrider dynasty, Kael'thas Sunstrider was the Prince of Quel'Thalas and a senior member of the Kirin Tor of Dalaran. After the death of his father, King Anasterian Sunstrider, and the destruction of most of Quel'Thalas, Kael'thas has led what remains of his people — first in the increasingly hostile Alliance, and then in the service of Illidan Stormrage — acting only for the benefit of his shattered homeland and its aggrieved people.
But Kael'thas now acknowledges a more sinister being as his master. Subsequent events have led him to betray Illidan, his own people, and existence itself... giving himself willingly to the service of the Burning Legion and its lord, Kil'jaeden the Deceiver.
Kael'thas has been described jokingly as the Team Rocket of Warcraft.