Rolo is the one who has been assigned from the Informatin Department to be Lelouch's brother. Obviously, this is not his real name, but he uses it from when he was a child and kill people. He has a GEASS in his right eye. It can stop time for the people he wants to, but it lasts just five seconds.
At the begin, he tries to kill Lelouch after finding out that he recovered his memories, but his "brother" conveinces him that he's really like a brother for him. Rolo has kinda strange feelings, but the thing he'd like the most to have is a family. He's shy with all, even if Lelouch, but when he kills someone, he's always cold.
He's obsessed with the locket that Lelouch gave him as a present for Nunnally's birthday, maybe inside of it, there's something he is very related to. He's trying to help Lelouch as he can, hiding all to the Information Department.
He's very skilled in piloting Knightmare Frames, and we can see it when he's inside the Vincent.