Tyson is a Cyclops, the son of Poseidon and his mother is unknown. Technically he is not a demigod, but at camp he lives in Percy's cabin, and is considered to be Percy's brother. He first appears in "The Sea of Monsters" as a homeless boy. He is afraid of Grover while Grover is also afraid of him. Also in "The Sea of Monsters" he was Percy's best friend and was always picked on. At the end of the book, he gets to go to work for his father, Poseidon, in the Underwater Armory.