Cerberus
Generation VI · Hound of Hades, warden of the dead
Cerberus, the many-headed hound of Hades — usually shown with three heads, a serpent's tail, and snakes bristling from his back — guards the gates of the underworld so that none of the dead may slip out. For his final and hardest labour Heracles wrestled the great dog barehanded and hauled him blinking into daylight, then dutifully returned him to his post below.