Cerberus in Heracles (Hercules): The Twelve Labors
Cerberus is the three-headed hound that guarded the gates of the underworld. He has three heads, a main of snakes, and lion's claws. (Yeah, so you probably won't find a pooch like him in your local pet store.) For his twelfth labor, Heracles has to wrestle the hellhound and bring him back to show Eurystheus.