Mark Harmon is best known for playing Special Agent Leroy Jethro Gibbs on the long-running action drama "NCIS." The actor was the show's headliner, having appeared from Season 1, Episode 1, and starring in over 400 episodes of the CBS hit.
Harmon was such an integral part of the "NCIS" family that CBS even included his biological son in the cast. According to IMDb, in several flashback sequences throughout the show, Harmon's son appeared as the young version of his dad.
Sean's collaborated on several big box office smash hits, including the Jim Carrey comedy "Dumb and Dumber To." He admits to having always had entertainment industry aspirations, having grown up around it.