A
winged
horse which sprung forth from the
stump of
Medusa's
neck after
Perseus decapitated her.
Was tamed by Bellerophon (with the assistance of a bridle given to him by Athena) to assist him in slaying the Chimera.
Later on, he tried to ride it up to Olympus, but Zeus stung Pegasus with a fly which caused it to buck and toss him off. Pegasus remained the bearer of Zeus' thunderbolts.
Its hoofprint in Castalia was in a spring which gave inspiration.