Deimos

Deimos is the god of terror and the son of Ares. He and his twin brother Phobos were responsible for stealing Ares charriot from Clarisse.

Percy Jackson and the Stolen Chariot
Angry that their sister was allowed to ride in Ares chariot, Phobos and Deimos decided to steal the chariot from her. They then hid it in the Statin Island Zoo, and used it as bait to catch their sister and Percy Jackson. He fought Percy but was defeated and disappeared.

Appearance and Powers
Deimos is described as a teenage boy, dressed in jeans, a black shirt, and a leather jacket.