NCIS and its characters were originally introduced in a two-part episode of the CBS television series JAG in . The show premiered on , 2003, in the United States. Created by Donald P. Bellisario and Don McGill, and executive produced by Bellisario, Shane Brennan, Gary Glasberg, and George Schenck & Frank Cardea, NCIS stars Mark Harmon as Supervisory Special Agent Leroy Jethro Gibbs, and Gary Cole as Supervisory Special Agent Alden Parker in charge of NCIS' Major Case Response Team. Based out of Washington, D.C., the team includes special agents Caitlin Todd (Sasha Alexander), Anthony DiNozzo (Michael Weatherly), Timothy McGee (Sean Murray), Ziva David (Cote de Pablo), Eleanor Bishop (Emily Wickersham), Alexandra Quinn (Jennifer Esposito), Nicholas Torres (Wilmer Valderrama), and Jessica Knight (Katrina Law), forensic specialists Abby Sciuto (Pauley Perrette) and Kasie Hines (Diona Reasonover), medical examiners Jimmy Palmer (Brian Dietzen) and Donald "Ducky" Mallard (David McCallum), medical examiners assistant Gerald Jackson (Pancho Demmings) and SIS attaché Clayton Reeves (Duane Henry). Operational psychologist Dr. Jacqueline Sloane (Maria Bello) assists the team during troubled times, while successive Directors Tom Morrow (Alan Dale), Jennifer Shepard (Lauren Holly), and Leon Vance (Rocky Carroll) command from on high. Series overview Episodes Introductory episodes The program and its characters are introduced during the eighth season of JAG. The JAG episodes, "Ice Queen" and "Meltdown", served as pilot episodes for the show. The character Special Agent Vivian Blackadder (Robyn Lively) does not appear in the series because producer Donald Bellisario felt that "she was a little soft for this kind of role". In , the two episodes were edited together and aired as "Navy NCIS: The Beginning". Season 1 (2003–04) Sean Murray (Timothy McGee) had a continuous arc starting with the seventh episode ("Sub Rosa"). Season 2 (2004–05) Sean Murray (Timothy McGee) was promoted to the main cast starting with the episode "See No Evil". Sasha Alexander (Special Agent Caitlin Todd) left the show after the season finale ("Twilight"). Season 3 (2005–06) Cote de Pablo (Ziva David) had a continuous arc starting with the first two episodes ("Kill Ari"), and later promoted to the main cast in the episode "Silver War". Lauren Holly joins the supporting cast as NCIS Director Jenny Shepard. She was promoted to the main cast in the ninth episode ("Frame Up"). This is the first season to feature 24 episodes. Season 4 (2006–07) Season 5 (2007–08) Rocky Carroll (Leon Vance) had a