Now this is an interesting one. Warcraft 3, in retrospect, might have entirely driven by the Jailer and his agents, all fighting each other to fit his ultimate purpose.
Kel'thuzad was the Jailer's right-hand man all along. Arthas was Zovaal's puppet, Sargeras and the Legion were puppets of the Dreadlords, who were also the Jailer's agents, and Sylvanas ultimately becomes the final key in all of his plans.
What a wild ride this one is!