Cerberus is the three-headed hound of Hades. He's the guardian watchdog of the Underworld - preventing the living from entering and the dead from escaping. Although, somehow Tanner and Andrew were able to pass by him and enter the Underworld. I'll have to remember to ask them how they did it. Orpheus charmed the beast with music, but the way those two sing, I doubt that's how they passed by (HA! HA!). The hound has snakes that grow out of his back that gave the appearance of a mane. He's the offspring of a pair of monsters, the half-woman half snake Echidna and the multi snake-headed Typhon. He's brother to three other multi-headed monsters, the Hydra; a two-headed dog; and the three-headed Chimera which had the head of a lion, goat, and snake. Tanner did tell me the Cerberus guards the Gate of Erebus, entrance to the Underworld. Both Tanner and Andrew did tell me how terrified they were to be in its presence, and from what I've read, I wouldn't want to be anywhere near it myself.