Stheno was Medusa’s immortal Gorgon sister, traditionally associated with exceptional strength.
Greek mythology usually names three Gorgons: Stheno, Euryale, and Medusa. They were daughters of Phorcys and Ceto, ancient marine deities. Unlike Medusa, Stheno and Euryale were immortal, so Perseus’s successful attack on Medusa did not destroy the whole group.
The name Stheno comes from a Greek root connected with strength or force. Mythological summaries often describe her as the strongest and most independent-minded of the Gorgons, although ancient sources provide fewer narrative details about her than about Medusa.
Stheno is easily confused with Euryale because both were immortal sisters whose stories are less developed. Medusa is the only Gorgon who receives a full death-and-transformation narrative in the best-known Perseus stories.