Cerberus

In Greek mythology, Cerberus is the three-headed watchdog who guards the entrance to the lower world, Hades. Originally, the dog was portrayed having fifty or hundred heads but was later pictured with only three heads. Cerberus permitted new spirits to enter the realm of dead, but allowed none of them to leave. Only a few ever managed to sneak past the creature, among which Orpheus, who lulled it to sleep by playing his lyre, and Heracles, who brought it to the land of the living for a while (being the last of his Twelve Labors). Great news for mythology aficionados: Cerberus lives!

found at The J-Walk Blog found at You Can't Make it Up