Calais, nicknamed Cal, is a son of Boreas and Orithyia. He is the brother of Zethes and Khione. He was a demigod until his father offered him and his brother Zethes immortality.

When Jason Grace, Leo Valdez, and Piper McLean come to see Boreas, he frequently suggests that he and his brother Zethes destroy them. He smells fire in Leo and claims, "Fire is bad," which makes Leo feel even less confident than before about his fire powers. He is instructed by Khione to wait with Leo while she takes Jason and Piper to see Boreas. When they return, he comments on how Khione isn't a very good person.