CerberusKerberos

An offspring of the monster Ekhidna (Echidna) and the snake-bodied Typhaon; he was the ferocious watchdog of the Underworld and was said to have fifty heads, a dragon tail and snakes writhing from his body; the artistic and written descriptions of Kerberos differ as to the number of heads but the common theme is constant in that he was a beast of untamed savagery who only obeyed the voice of Hades (lord of the Dead) or his bride, Persephone.

Kerberos stands at the gates of the House of Hades and fawns on the dead as they enter but will savagely eat anyone trying to pass back through the gates and return to the land of the living.

To complete his Twelfth Labor, Herakles (Heracles) was required to descend into the Underworld and bring Kerberos to the surface; Herakles descended into the Underworld and confronted his uncle, Hades. Either through consideration for Herakles or intimidation by Zeus’ wrath, Hades agreed to let Herakles temporarily take Kerberos into the sunlight on the condition that no weapons be used to subdue the beastly hound; when Herakles presented Kerberos to his cousin and taskmaster, Eurystheus, he hid in a giant urn in the ground.

His name may also be rendered as Kerberos or Cerberus.

• Theogony, lines 311 and 769