Thomas Mark Harmon (born September 2, 1951) is an American television and film actor who has appeared in a wide variety of roles since the mid-1970s. Since 2003, Harmon has starred as former U.S. Marine Corps Gunnery Sergeant and Sniper turned NCIS Special Agent Leroy Jethro Gibbs in the hit CBS series, NCIS, a role that has become Harmon's best-known role to date while also giving him international recognition.