The original cast of "NCIS" included Mark Harmon, Michael Weatherly, Pauley Perrette, David McCallum and Sasha Alexander. Sean Murray and Brian Dietzen served as recurring characters in the show's first season, but were eventually promoted to starring roles.
"NCIS" premiered in Sept. 2003, and has consistently been one of the most popular shows on television. As of June 2015, original cast members Mark Harmon, Michael Weatherly, Pauley Perrette and David McCallum continue to serve as the lead actors on "NCIS." Sasha Alexander was one of the lead actors for the show's first two seasons, but she left the show after the second season. Alexander reprised her role as a guest star in the third and eighth seasons of "NCIS."
Some actors began the show playing smaller roles, but received large roles as "NCIS" became a success. Sean Murray, who played a recurring character in the first season, was promoted to series regular in the second season. Brian Dietzen was promoted to the main cast in the tenth season, after serving as a recurring character for the first nine seasons. Though not part of the original cast, actors such as Rocky Carroll, Cote de Pablo and Lauren Holly have been added to the cast of "NCIS" over the course of the show.