Jamil Walker Smith is an American actor, director, producer and writer. His best known role is as the voice of Gerald, a fourth grader and Arnold's best friend in the Nickelodeon animated TV series Hey Arnold! He also appeared on several shows like Sister, Sister; Girlfriends; Bones; The X-Files; and The Bernie Mac Show. He is an actor by trade and writes, acts and directs his own short film projects. He played Master Sergeant Ronald Greer in both seasons of Stargate Universe.