Tyson

Tyson is a Cyclops, whom are technically all half-brothers of Percy Jackson. Though Percy is at first disgusted to realise that he was related to him in "The Sea of Monsters", he completely changes gears by the end of the book. As such, Tyson is closer to Percy than any of his brethren, and Percy even once announced that Tyson was his "baby brother" when he won the chariot race due to Tyson's help in constructing the equipment. Due to the effect of The Mist, Tyson looks he has two eyes to people outside of Camp Half-Blood, although when Sally Jackson asked Percy what he saw when he looked at Tyson's eyes he was unsure, as the mist naturally made him not want to look at his eyes.

The Sea of Monsters
Tyson appears as Percy's only friend in Percy's new school. Tyson deflects fiery celestial bronze dodgeballs fired by the Laistrygonians at Merriweather Prep. Tyson joins Percy and Annabeth in their quest by traveling the Hippocampis Poseidon sent. He boards the Princess Andromeda. After escaping along with Percy and Annabeth, they battle a hydra at some island, but are saved from Clarisse and her ship, the CSS Bermingham. Tyson also tries to fix the engine on the CSS Bermingham when it explodes. Percy thinks he is dead, but just when Percy is about to be killed by Polyphemus, Tyson comes in and saves him. After getting the Golden Fleece, Tyson and the others get saved by the Hippocampi. Captured by Luke, Tyson starts beating up some demons and is saved along with Percy and Annabeth by Chiron and his relatives. At the end, Tyson is summoned to the Cyclops Forges in Poseidon underwater palace.

The Titan's Curse
He has only been mentioned in an Iris Message. Although it is also mentioned that he wants to take a vacation and visit Camp Half-Blood in the summer.

The Battle of the Labyrinth
He is seen cleaning the Poseidon cabin for inspection early on in the book. He then accompanies Percy, Annabeth, and Grover in their quest into the Labyrinth to find Pan, and to find Daedalus so he can help them save the camp from an invasion led by Luke and his army.