Medusa

Only mortal of the three Gorgon sisters — Stheno, Euryale, and Medusa — who dwelt at the edge of night beyond the stream of Ocean. In the Hesiodic tradition she is monstrous from birth, and Poseidon lies with her in a soft meadow among spring flowers. Perseus, guided by Hermes and armed with Athena's polished shield, approached her by her reflection and struck off her head while she slept; from her severed neck sprang at once the winged horse Pegasus and the giant Chrysaor, the children Poseidon had fathered on her. Her head kept its petrifying power after death and became the Gorgoneion on Athena's aegis. The Roman variant in which Medusa is a raped mortal woman transformed in punishment by Athena belongs to Ovid's Latin retelling, not the Greek sources.