Who is Neilus Aran in World of Warcraft

Niles Aran is the father of Medivh, currently the last Guardian of Tirisfal. While his whole story is not clear, it is known he was a mage of the Kirin Tor, and eventually died a violent death. His spirit is locked inside the library of Karazhan, mad with rage and despair, attacking all who enter his sanctum.