Lelouch's younger brother, and also a student at Ashford Private Academy. However, that was his fake identity. He was actually an assassin hired by the Intelligence Service to watch over Lelouch.
But he was won over by Lelouch, because he felt that Lelouch understood his complicated origins as an assassin.
He had the Geass power that stopped time, but when he used it, it put a lot of strain on his heart. He used his Geass past its limits in order to rescue Lelouch, who had been betrayed by the Black Knights. After they both escaped, he died in Lelouch's arms.