In Hesiod’s Theogony, Phorcys is named as Medusa’s father.
Phorcys was an ancient sea deity and one of the primordial marine powers in Greek mythology. Hesiod presents him as the son of Pontus, the sea, and Gaia, the earth. His consort was Ceto, another sea deity, and their children included several groups of dangerous or monstrous beings.
Medusa was the only mortal child traditionally attributed to Phorcys and Ceto. Her sisters Stheno and Euryale were immortal Gorgons. This family connection links the Gorgons with the Graeae, Echidna, and other creatures in the mythological genealogy of Hesiod.
Later writers sometimes changed or expanded Medusa’s story, especially her relationship with Poseidon, who was described as the father of Pegasus and Chrysaor. That later role does not replace Phorcys as Medusa’s paternal parent in Hesiod’s genealogy.