Mark Harmon and "NCIS" have been synonymous for the majority of the show's run. He played Leroy Jethro Gibbs in a whopping 435 episodes, not to mention his appearances in "JAG" and "NCIS: New Orleans," which bring the total to 441. Harmon's final appearance as Gibbs was in "NCIS" Season 19, but he will continue as a producer. While he has left the main cast, the show's producers and Harmon himself have expressed interest in his return. The question is not if, but when Gibbs will make a comeback.