Pegasus is a

Mythical winged divine horse, and one of the most recognized creatures in Greek mythology. Usually, he is depicted as pure white. Greek myths about him vary as they evolve and reflect progression through successive generations of deities. In Archaic Greek mythology, Pegasus is the offspring of the Gorgon Medusa, when she was depicted as a mare. In later myths, Pegasus was given birth by Medusa as she was dying, while being decapitated by the hero Perseus. In Classical Greek mythology, the Olympian god Poseidon is identified as the father of Pegasus. Pegasus is the brother of Chrysaor and the uncle of Geryon. Pegasus was caught by the Greek hero Bellerophon near the fountain Peirene with the help of Athena and Poseidon. Pegasus allowed Bellerophon to ride him in order to defeat the monstrous Chimera, which led to many other exploits. Bellerophon later fell from the winged horses back while trying to reach Mount Olympus, where the deities resided. After that failed attempt, Zeus transformed Pegasus into the eponymous constellation.

Source Wikipedia