Chrysaor

Chrysaor (Greek: Χρυσάωρ, Khrusaōr) is 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, Titan of the sea. 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 sacred 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 Oceanus, and 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.

The Sea of Monsters
Gus a son of Hermes stole a pair of fuzzy dice from Chrysaor's Honda Civic in 1988.

The Mark of Athena
Chrysaor and his crew attack the Argo II in the Mediterranean Sea. They intend to sell Piper and Hazel to Circe, kill Jason and then give Annabeth and Percy to Gaea. Chrysaor also appears to think Annabeth is pretty as he is alway calling her lovely Annabeth. Chrysaor batttles Percy on the deck of the Argo II. Percy is unable to defeat him alone but once his crew abandons him, Percy and the other members surround him. Chrysaor is knocked off the Argo II by Frank into the water. Percy decides not to follow him since he doesn't know the waters and Chrysaor is too powerful.