Monsters From Greek Mythology

The hound of Hades is sometimes shown with two heads and various body parts, but the most familiar form is the three-headed Cerberus. While Cerberus, one of Echidna's children, is said to be fierce enough that the gods fear him, and flesh-eating, he is a watchdog in the land of the already dead.

One of Hercules' tasks was to fetch Cerberus. Unlike the monsters that devastated the countryside, which Hercules destroyed, Cerberus did not have to be killed first. Instead, he was returned to his guard post.