Medusa (mədōˈsə) [key], in Greek mythology, most famous of the three monstrous Gorgon sisters. She was once a beautiful woman, but she offended Athena, who changed her hair into snakes and made her face so hideous that all who looked at her were turned to stone. When Medusa was with child by Poseidon, Perseus killed her and presented her head to Athena. Chrysaor and Pegasus sprang from her blood when she died. Medusa's head retained its petrifying power even after her death. Because of this power, her image frequently appeared on Greek armor. In some myths Athena used the Medusa head on her aegis.
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