Eurystheus ordered Herakles to bring him Kerberos, a three-headed dog-like monster with a dragon's tail and a mane of poisonous snakes. It guarded the entrance to the Underworld. The three heads could see the past, present, and future. Some say they represented birth, youth, and old age. Kerberos allowed the dead to enter the Underworld, but anyone who tried to leave was eaten. Kerberos was the offspring of Echidna, a monster part woman/part snake, and Typhon, a fire-breathing giant. Kerberos' brother was the two-headed dog Orthrus. 