Medusa is one of the three Gorgon sisters (with Stheno and Euryale), and the only one who was mortal; her hair was living snakes and her gaze turned any who met it to stone [S4][S5]. In the standard account (Ovid, building on earlier tradition) she was a beautiful maiden transformed into a monster (in Ovid, for her hubris and for an offense against Athena), and she was slain by Perseus, who used Athena's mirror-shield to avoid meeting her gaze [S5]. (In Hesiod's earlier Theogony the Gorgons are monstrous from the start, daughters of the sea-gods Phorcys and Ceto — the 'beautiful maiden' version is later, from Ovid.) [S1][S5] From her severed neck sprang the winged horse Pegasus and the giant Chrysaor [S1][S5].