It's been more than 20 years since NCIS premiered as a backdoor pilot on JAG - and the genre of criminal investigation series has never been the same. NCIS debuted in 2003, following Mark Harmon's Leroy Jethro Gibbs and his team of rowdy and somewhat green Naval Investigators - including Michael Weatherly's Anthony "Tony" DiNozzo and Sean Murray's Timothy McGee - as they found justice and answers for those killed or affected by crimes in the armed forces.