Medusa was the mortal Gorgon in Greek mythology, while her sisters Stheno and Euryale were immortal.
The three Gorgons were daughters of the ancient sea deities Phorcys and Ceto. In Hesiod’s Theogony, Medusa is specifically distinguished from her sisters because she alone could die. Later Greek and Roman stories made Medusa the best-known Gorgon because the hero Perseus killed her.
Medusa’s gaze was said to turn anyone who looked directly at her into stone. Perseus avoided this danger by looking at her reflection in a polished shield while striking off her head. Her severed head retained its petrifying power and was later used by Athena.
A common mix-up is assuming that “Gorgon” means Medusa alone. Gorgon is the group name; Medusa is one member of the three-sister group.