In Greek mythology, Cerberus , often referred to as the hound of Hades, is a multi-headed dog that guards the gates of the Underworld to prevent the dead from leaving. Cerberus was the offspring of the monsters Echidna and Typhon, and is usually described as having three heads, a serpent for a tail, and snakes protruding from multiple parts of his body. Cerberus is primarily known for his capture by Heracles, one of Heracles' twelve labours.