Medusa was one of three gorgon sisters along with Euryale and Stheno, who all lived at the edge of the world. It is most commonly agreed that the three were children of Phorcys and Ceto. Although her sisters were immortal, Medusa was not. Not much is recorded concerning Stheno and Euryale, and are not noted to have any major role in Medusa's life. She is mentioned in Ovid's narrative poem, "Metamorphoses". Her name means "to protect, to rule over".
Medusa was devoted to Athena, the goddess of war and wisdom, and had been a priestess at a shrine dedicated to the Goddess while living a simple life. Like Athena, a virginal goddess, Medusa had also committed to a life of chastity. Unlike her two sisters, Medusa was not born hideous, but rather beautiful. Ovid describes her beauty, praising her hair in particular and describing it as "golden ringlets wav'd and graceful" (Ovid).
Medusa's beauty did not go unnoticed. According to Ovid, her beauty could attract a crowd of envious men vying for her attention. However, it was not only common men that took notice of Medusa, but also the God of the Sea, Poseidon. Being a god, seeking Medusa's affection as well. Poseidon had no care for whether Medusa paid mind to him nor if she felt the same desire towards him that he harbored for her.
Instead, he forced himself upon Medusa in Athena's shrine thus angering the Goddess for desecrating it. Seeking vengeance, rather than punish Poseidon, Athena cursed Medusa so that snakes would grow from her head in place of her hair. Stripped of her beauty, Medusa was left with an appearance so hideous and frightful that anyone who saw her was turned to stone.
Perseus, a demi-god and son of Zeus, was sent by Polydectes, the king of Seriphus to bring him Medusa's head. Medusa posed no threat to the King nor his kingdom, yet Polydectes gave Perseus this quest in order to pursue Perseus' mother as it would force distance between Perseus and his mother because Perseus did not condone and actively sought to pose as an obstacle to Polydectes' advances towards his mother. The quest was meant to be a suicide mission, but Perseus was aided by the gods: he was given the Cap of Invisibilty from Hades, a pair of winged sandals from Hermes, and a reflective shield from Athena. With these gifts, Perseus beheaded Medusa, and from her body sprang the winged horse Pegasus while her blood that flowed from her body and touched the earth turned into serpents. Medusa's head was used further by Perseus on his adventures as her powers of petrification did not cease in her death. Her head was later worn on Athena's aegis.