Pegasus springs from the neck of Medusa when Perseus beheads her, in Hesiod's account, together with his brother Chrysaor, the offspring, in the myth, of an earlier union with Poseidon, god of horses. His central story is with Bellerophon, whom he carries against the Chimera and who is thrown to ruin when he presumes to ride up to Olympus; Pegasus completes the ascent alone and becomes the bearer of Zeus's thunderbolts, later set among the stars as a constellation. A secondary tradition makes him the maker of the spring Hippocrene ("horse fountain") on Mount Helicon, struck from the rock by his hoof, which links him to the Muses and to poetic inspiration. That association is why "Pegasus" recurs as an emblem of poetry and soaring imagination, a usage that draws on one strand of the myth and leaves the tragic Bellerophon story aside.
Pegasus was also, from an early date, a civic emblem rather than purely a mythic figure: the coinage of ancient Corinth, Bellerophon's own city, carried his image for centuries, one of the most widely circulated equestrian types in the Greek world, precisely because the local hero's winged horse gave Corinth a recognisable badge distinct from every rival city's coin types. That civic and heraldic use anticipates, without directly causing, Pegasus's much later adoption as an emblem of inspiration and swift achievement in European and American commercial and institutional branding, a modern afterlife that draws on the Hippocrene strand of the myth while leaving Bellerophon's fall from grace, the myth's own original warning against presumption, almost entirely forgotten.