Originally Posted by Majere
C'Thun is the only one of the Old Gods to be named so far, having received that name from his servants, the Qiraji. He was defeated in Silithus in a battle which also resulted in the defeat of a Titan. C'Thun was believed to have been permanently defeated, but reemerged as the driving force behind the Qiraji. He is trapped deep beneath the ruined temples of Ahn'Qiraj, where he has exerted his will for thousands of years over the Qiraji, who in turn command the Silithid.
According to the War of the Ancients Trilogy, there are three Old Gods still living, imprisoned and chained by the Titans deep beneath the surface of Azeroth.