Medusa

Medusa was the most beautiful of the three gorgons and the only one who was mortal. She loved Poseidon and when she met with him in the Temple of Athene the building was desecrated. She was punished by having her hair turned into snakes and by being so ugly that any mortal who looked at her would be turned to stone. Perseus cut off her head while she slept and then presented it to Athene.