Greek Mythology: Pegasus is the offspring of Poseidon and Medusa, Medusa conceived him and his brother while Poseidon raped her on the steps of the temple of Athena. Medusa was a priestess of Athena. Athena watched as Poseidon raped then turn her into the Gorgon Medusa after Poseidon was done with her. Medusa gave birth to her sons when the hero Perseus cut off her head.