|“||The dragon must be deactivated. We can’t have fire in here. The heat ruins my hair.||”|
–Zethes, in The Lost Hero
Zethes is a son of Boreas and Orithyia, and the brother of Calais. His sister, Khione, is the goddess of snow. He was a Greek demigod until his father offered him and his brother, Calais, immortality. He traveled to retrieve the Golden Fleece with the original Jason, on the original Argo.
Zethes and his brother Calais were once Argonauts, travelling with Jason to retrieve the Golden Fleece. The Argonauts eventually found Phineas on his island. Phineas had prophesied that the Boreads would help rescue him from his punishment by killing the Harpies. Zethes was unsure about helping him escape his divine punishment, as he feared the wrath of the gods. Zethes and Calais would have killed the Harpies if the goddess Iris had not intervened.Leo Valdez describes Zethes as a teen who looks like a "love god from one of his mom's 1980's rock album covers". He has a bad case of acne and his shirt is unbuttoned too low. He and his bother Calais allow Leo, Piper McLean, and Jason Grace into Boreas' home.
Zethes is obvious in his attempts to impress Piper, often commenting that she is very pretty, and when she loses the blessing of Aphrodite, he offers her some of his own beauty products, which she promptly refuses.
Zethes and his sister Khione both want the demigods turned into ice statues (so Khione could keep Jason, and Zethes could keep Piper) but their father Boreas refused, wishing to let them go. As they leave, Zethes and Cal warn them to be careful, especially when Jason insults Khione, because she never forgets insults.
Zethes, along with Calais and his sister, Khione appear on the Argo II. He speaks in French to Piper, which she translates easily because she is a daughter of Aphrodite. He has claims her as his own and states that he wants to marry her. After Piper reactivates Festus' head, Festus incinerates both Zethes and Calais and Piper keeps his sword as her own.
- Cryokinesis: As a son of Boreas, he can control and manipulate the cold, though not to the same extend as Khione.
- He can freeze things.
- He can control blizzards and snowstorms.
- He can make icy winds blow something out of the air.
- Aerokinesis: As a son of Boreas, he can control and manipulate the air.
- He can ride air currents, making him fly.
- He can control, and generate very powerful winds.