The lone mortal of the three Gorgons. Medusa had sexual intercourse with the god Poseidon in the temple of Athena. Outraged, Athena turned Medusa into a Gorgon.
Perseus, in his quest to find a fitting wedding gift, killed Medusa with the aid of Hermes, Athena and Hades. Hermes gave to Perseus a sword, which could penetrate Medusa's golden scales. Athena gave him a shield of polish bronze. Hades gave him a helmet, which turned the wearer invisible. Perseus used the shield as a mirror, so as not to be turned into stone, and used the sword to behead the Gorgon. The two sisters could not find Perseus and avenge their sisters death, for Perseus was wearing the helmet and thus invisible.
When Medusa was killed, the winged horse Pegasus and Chrysaor, sprung forth, presumably the unborn children of Medusa and Poseidon.
Her head was eventually given by Perseus to Athena, who fixed it upon her shield, called the aegis.