The origins of Pegasus, the mythical winged horse, are entwined with various other ancient myths. It can be tracked back to the story of Poseidon who, taking the form of a horse (or in some versions a bird), seduced Medusa in a temple dedicated to Athena. Athena was offended by this this sexual use of her temple, so she turned Medusa's hair into serpents. Later, when Perseus decapitated Medusa, Pegasus was born of Medusa's blood.
Pegasus became the mount of Bellerophon after being caught with the aid of a golden bridle given to him by Athena. What is lesser know is that Bellerophon was originally called Hipponous (Hippo means horse in Greek), the son of Glaucus who was a ghost known to frighten horses.
When Bellerophon attempted to fly Pegasus to Mount Olympus he was dismounted by Zeus. Pegasus continued on and made it to Mount Olympus. Here Pegasus spent his days carrying lighting bolts for Zeus.