Chrysaor

Chrysaor (Greek: Χρυσάωρ, Khrusaōr) was the brother of Pegasus, and the son of Poseidon and Medusa. Chrysaor and Pegasus were not born until Perseus chopped off Medusa's head. Chrysaor had one son, Geryon, from Callirrhoe, daughter of Oceanus. He appears as one of the villains in The Mark of Athena.

History
Medusa, one of the Gorgon sisters, the most beautiful, and the only mortal one, offended Athena by having relations with Poseidon in one of Athena's temples. Chrysaor and Pegasus were said to be born from the drops of Medusa's blood which fell in the sea; others say that they sprang from Medusa's neck as Perseus beheaded her, a "higher" birth (such as the birth of Athena from the head of Zeus).

Chrysaor, married to Callirrhoe, daughter of glorious Oceanus, was father to the triple-headed Geryon, but Geryon was killed by the great strength of Heracles at sea-circled Erytheis beside his own shambling cattle on that day when Heracles drove those broad-faced cattle toward holy Tiryns, when he crossed the stream of Oceanos and had killed Orthos and the oxherd Eurytion out in the gloomy meadow beyond fabulous Oceanos.