Medusa is the Gorgon with snakes for hair whose gaze turns people to stone.
Medusa was one of three Gorgon sisters, alongside Stheno and Euryale. Unlike her sisters, she was mortal. Greek mythology generally describes her as having living snakes in place of hair and a terrifying face whose direct gaze petrified anyone who looked at her. Her parents were the ancient sea deities Phorcys and Ceto.
The hero Perseus was sent to obtain Medusa’s head. Because looking directly at her was fatal, he used a polished shield to view her reflection and decapitate her. He later used the severed head as a weapon, including against the sea monster threatening Andromeda, before giving it to Athena, who placed it on her shield or breastplate.
A common mistake is treating Euryale or Stheno as alternate names for Medusa. They were separate Gorgons, though both were immortal. Another mix-up comes from later retellings that portray Medusa as a beautiful woman cursed by Athena; that version is especially associated with the Roman poet Ovid rather than the earliest Greek traditions.