Cerberus was the guard dog of the underworld. He had the serpent's tail and three dog-like heads, so at least one head would always be awake to guard the entrance. He protected the gates of Hades from living people seeking to enter, as well as dead people seeking to leave without permission from a deity (although Cerberus was especially fond of a certain kind of honey-cake which he accepted as a bribe for permitting entrance or exit; Aeneas and Psyche used this method to escape from Hades.) Cerberus was the son of Enchinda and Typhon, and his siblings included the Sphinx, the Hydra, and the Nemean Lion. Enchinda, his mother, was half serpent and half woman. It is said that she is related to Medusa, the snake-haired demon who turned mortals to stone. His fearsome father, Typhon, was a serpent-covered giant who breathed fire, and threw mountains at gods. Typhon fought Zeus in an apocalyptic battle in which Zeus struck down one of Typhon's mountains onto Typhon himself, crushing him for eternity.
For his 12th and final Labor, Hercules had to go to the underworld and fight Cerberus. Hercules strangled all three of Cerebrus's heads at once, and took the limp Cerberus to the world of the living, so he could prove he had completed the task. Afterwards, Cerberus was released back to his post. Also, Orpheus had a brief encounter with Cerberus. Orpheus descended to get his lover Eurydice, but Cerberus stood in the way. Orpheus played his lyre and lulled Cerberus to sleep, and so managed to sneak by him.
by Roddy Lindsay, St. Paul's School, Jan 12 2001