Fathered by Poseidon with Medusa, Pegasus was born, wings and all, when Medusa was relieved of her head by Perseus. Pegasus then galloped away, down Mount Helicon, and his steps created the well Hippocrene, which became sacred to the Nine Muses.
Pegasus’ story is closely intertwined with that of Bellerophon, an adventure-seeking youth, who got exactly what he sought, with the help of Pegasus. Given a golden bridle by Athena, Bellerophon captured the magical, flying horse, and they set off to pursue and slay the dreadful Chimera. For this deed the King of Lycia gave his daughter as wife to Bellerophon, and the couple was happy for many, many years.
Bellerophon, forever seeking greater and greater adventures attempted to ride Pegasus up Mount Olympus. This greatly offended Zeus, who caused Pegasus to bolt and throw his rider to earth.
Their stories have vastly different endings. Pegasus, loved by Zeus and in charge of bringing him his lightening and thunderbolts, was eventually made one of the most beautiful constellations in the heavens. Bellerophon, crippled in his fall to Earth, although Zeus allowed him to land on soft ground, spent the remainder of his life grieving the loss of his steed, and wandering the Earth in search of him.