Anthony D. "Tony" DiNozzo, Jr. is a fictional character from the CBS TV series NCIS portrayed by American actor Michael Weatherly. An original cast character created by producer Donald P. Bellisario, he is credited in episode 306, but actually appearing in 305 of the series. He has also made guest appearances on the spin-offs NCIS: Los Angeles and NCIS: New Orleans.
Tony DiNozzo, born in 1972 (as guessed correctly by Caitlin Todd in the season 1 episode Split Decision) is the senior field agent of the fictional Major Case Response Team (MCRT) led by Leroy Jethro Gibbs (Mark Harmon) a former Marine Gunnery sergeant. The team investigates major crimes involving military personnel, often dealing with local law enforcement officers (LEOs). A former police detective, he is characterized as an outgoing, joking, charismatic former jock and frequent lothario. His charisma helps him do undercover work and to deal with intra-agency conflicts. He often leads the team's crime scene investigations, where medical examiner Dr. Mallard (David McCallum) would put him through physical exertion for evidence retrieval. Over the course of the series, he carries a few storylines, including an undercover assignment that goes through seasons four and five to catch an international arms dealer. DiNozzo provided some comic relief for an otherwise serious drama, regularly spouting movie trivia, especially in the early seasons, and as a Casanova, his dating provided many roguish experiences. The death of agent Caitlin Todd and DiNozzo's relationship with agent Ziva David become fundamental to his subtle shift in attitude and character development.
(Souce: Wikipedia)
