When Bellerophon was still a boy growing up in Corinth, he had yearned to ride the magic horse Pegasus, immortal offspring of the god Poseidon and the Gorgon Medusa. Pegasus was born when the hero Perseus cut off Medusa's head. Like everyone else, Bellerophon had been unable to so much as approach Pegasus. So he sought the advice of the seer Polyeidus.