Kerberos, sometimes called Cerberus, was a fearsome looking hellhound that guarded the gates of Hades. Its only purpose was to prevent damned souls trapped in the underworld from escaping. Kerberos is believed to be the offspring of the goddess Echidna and the fire-breathing primordial giant, Typhon.
It is described as a three-headed dog with a mane of serpent heads, a snake for a tail, and the lion claws extending from his paws. As the final task assigned him by King Eurystheus, Hercules had to capture Kerberos alive without using any weapons.
Image credit - Vyrilien