Cerberus is Hades's three-headed big dog. He guards the entrance to the Underworld to keep any of the dead from escaping and any of the living from entering. He once escaped from his post and Hercules went to the Underworld to find him and get him back where he belonged. (Hercules in the Underworld) Hercules encountered Cerberus again when the hero was sneaking into Hades's castle to rescue Persephone. Cerberus recognized him and let him pass without incident seeing as Hercules promised not to hurt him. (HTLJ "The Other Side")
- Though it's never stated on-screen, Cerberus is probably one of the children of Echidna and Typhon, as in mythology. Their son, Obie, has a stuffed toy of Cerberus in "Monster Child in the Promised Land".
- The name "Cerberus" has been suggested to derive from a very old Proto-Indo-European root meaning "Spotted".