Greek Mythology : Medusa.

One of the Gorgons, the only mortal one. She had a ghastly face that turned anyone who looked at it to stone, a dragon body and snakes for hair. Her parent's were Phorcys and Ceto, and she lived by the western ocean with her immortal sisters Stheno and Euryale.
She was killed by Perseus, and from her blood and Poseidon's semen the horse Pegasus was born.The head of the Gorgon was often used in Art. It was pictured on the aegis of Athena, since Perseus had offered it to the goddess after his feat, and people would have it as door knockers to protect the house from evil and it was also painted or sculptured inside cups.
According to another story Medusa was originally a lovely maid who was the daughter of Echidne, who was half woman, half snake, and Typhon, the worst monster in the world. Poseidon fell in love with her, and seduced her in the temple of Athena. Because this was sacrilege, the goddess Athena wanted revenge. She could not punish Poseidon since he was a greater god, so all the blame fell on Medusa,who turned into a monster.