Mark Harmon officially ended his run as a series regular on CBS’ long-running procedural drama "NCIS" Monday. The latest episode acted as a goodbye for Harmon’s character, Special Agent Leroy Jethro Gibbs, who has been with the series for the past 18 years after first being introduced on the show "JAG" in 2003. According to Deadline, Monday’s episode, "Great Wide Open," saw Gibbs and Special Agent Timothy McGee, played by Sam Murray, venture to Alaska to find a contract killer who was hired by