Cerberus . . . or did he?

Cerberus, of myth, was an enormous 3-headed dog who guarded the gates of Hades (realm of the dead). In Clash of the Titans, on the other hand, Cerberus is a 2-headed wolf who hangs out in some ruins being a jerk. Which is the real truth? Only a Gallup poll could know for certain. And they haven't done one.