Di Nozzo is known for his seemingly-endless film references; Ziva insists that his dying words will be "I've seen this film".
He attended Ohio State University as a physical education major and was a member of the "Alpha Chi Delta" fraternity, class of 1989.
After serving in Panama and Iraq, he retired from the Marine Corps with the rank of Gunnery Sergeant.
He joined NIS, which later became NCIS, after his wife Shannon and only daughter Kelly were murdered in 1991.
During the course of season four, he is on an undercover assignment that Director Jenny Shepard leads, the key mission being to find arms dealer La Grenouille by posing as his daughter's boyfriend, but he ends up falling in love with her.
In the episode "Knockout", he reveals that he is not doing well with women and that he is still hurting from his relationship with Jeanne Benoit.
He later travelled to Mexico and murdered the drug dealer responsible, a crime he kept concealed for twenty years.
Since then, he has been married and divorced three times, and is single, although he has had a number of romantic relationships since his last divorce.
("Frame Up") Di Nozzo is a flirt, and has a fondness for playing pranks on his co-workers, sometimes with little respect for their boundaries.
Todd is a former Secret Service agent, recruited by Gibbs after she successfully helped him solve a murder aboard Air Force One.
She works well with everyone on the team, becoming particularly close with Ducky and Abby, who convinces her to get a tattoo.
Harmon is one of two actors to appear in every episode of NCIS.
Special Agent Caitlin "Kate" Todd (Sasha Alexander) first appears in the episode "Yankee White".