An organization led by the most powerful human mages in the world. They founded the city of Dalaran as a place to study and teach the ways of magic. one of their task was to safeguard and wield the Eye of Dalaran
Sometime later, the term "Kirin Tor" refered to the Magus Senate of Dalaran, and later to the high council of that body which consisted of five to seven members only. (In "Day of the Dragon" there are six members of the Kirin Tor. "The Last Guardian" mentions seven and lists five by name. Antonidas, Jaina and Kel'Thuzad are the only ones mentioned in the games.)
However, some mages of the Kirin Tor delved too deeply into necromancy, demonology, and other warlock magics. One of the most powerful, Kel'Thuzad, left the Kirin Tor to open a rival school of necromancy: the Scholomance. There, he and his students created the Plague of Undeath, which ravaged Azeroth and led to the rise of the undead Scourge. Kel'Thuzad himself became a powerful Lich, and chief lieutenant to the Lich King.
What is left of the Kirin Tor strive to rebuild their once magnificent capital of Dalaran.