Leroy Jethro Gibbs is a fictional character and the original protagonist of the CBS TV series NCIS, portrayed by Mark Harmon. He is a former U.S. Marine Corps Scout Sniper turned special agent who commands a team for the Naval Criminal Investigative Service. Gibbs is the most accomplished marksman on the team and the most skilled at handling violent standoffs; he depends on his other agents heavily for technical forensics and background checks. He is patient but firm with his team and has little patience for bureaucracy; he commands most other main characters—including his current staff Timothy McGee, Nick Torres and, briefly, Jessica Knight and previous staff Caitlin Todd, Anthony DiNozzo, Ziva David, Alexandra Quinn, Clayton Reeves, Ellie Bishop and Jacqueline Sloane.

NCIS is an American military police procedural television series and the first installment within the NCIS media franchise. The series revolves around a fictional team of special agents from the Naval Criminal Investigative Service (NCIS), combining elements of the military drama and police procedural genres with comedy. The concept and characters were initially introduced with two episodes of the CBS series JAG ; as a spin-off from JAG, the series premiered on September 23, 2003, on CBS. To date, it has entered into the 21st full season and has gone into broadcast syndication on the USA Network. Donald P. Bellisario and Don McGill are co-creators and executive producers of the premiere member of the NCIS franchise. As of 2022, NCIS is the third-longest-running scripted, live-action U.S. prime-time TV series currently airing, surpassed only by Law & Order: Special Victims Unit (1999–present) and Law & Order ; it is the seventh-longest-running scripted U.S. prime-time TV series overall.