Medusa

Medusa was one of the three Gorgons, daughters of Phorcys and Ceto, sisters of the Graeae, Echidna, and Ladon – all dreadful and fearsome beasts. A beautiful mortal, Medusa was the exception in the family, until she incurred the wrath of Athena, either due to her boastfulness or because of an ill-fated love affair with Poseidon. Transformed into a vicious monster with snakes for hair, she was killed by Perseus, who afterward used her still potent head as a weapon, before gifting it to Athena.
Source: https://www.greekmythology.com/Myths/Creatures/Medusa/medusa.html