Tyson

At his introduction, Tyson is a childish and clumsy Cyclops who is known for crying and at times appears to be dense at a glance. Sometimes he forgets his own strength (e.g. when he hugs Percy, who feels as if his ribs are breaking). Tyson is somewhat naive in The Sea of Monsters as Polyphemus is able to trick him into lowering his defenses. He is also not sure of himself, as seen in The Sea of Monsters.

In spite of his naiveté and seeming density, Tyson is smarter than he seems and very determined. In The Battle of the Labyrinth, he has matured, though he still retains his innocence. He noticed the real reason why Percy cannot tell anyone about Nico being the son of Hades. Tyson's earnest attitude reminds Briares who he really is and decides to help Camp Half-Blood as a result.

Tyson cares a great deal about his friends and is willing to risk his life for them if necessary. He shows a strong love for pegasi and hippocampi (which he calls "chicken ponies" and "fish ponies" respectively), though the former are nervous around him. In order to protect himself and his friends, Tyson began to take on the stance of a leader in The Last Olympian and becomes less of a child in Poseidon's eyes as well.

Tyson, the Son of Poseidon. He is yes indeed Percy's younger brother, although not a demi-god, but a Cyclops. Tyson is a tall, strong, one-eyed, loving brother. He is six-foot-three.