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".Di Nozzo's mother was over-protective and she "dressed him like a sailor until he was ten".
Di Nozzo is said to have played college basketball, "running the point for Ohio State" according to Abby.
It is mentioned in the season three episode "Kill Ari (Part I)" that he comes from a wealthy family but has been cut off by his father, Anthony Di Nozzo Sr (played by Robert Wagner who in turn was played by Weatherly in a TV movie).
However, Todd's relationship with Di Nozzo is more adversarial and they are more like siblings than anything else.
Tony frequently flirts with her and sometimes goes through her personal belongings, no matter how many times she points out that his behavior is grossly unprofessional.
Both are rescued from the elevator and survive their ordeal.
In season thirteen, Di Nozzo confesses his love for Ziva after learning of her apparent death, and it is revealed that the two have a child named Tali.
In "Truth or Consequences", Gibbs saves his entire team by shooting the leader of a terrorist cell after Di Nozzo and Mc Gee get captured looking for Ziva.
In the episode "Extreme Prejudice", Gibbs goes after Harper Dearing, cornering the terrorist in a home in West Virginia, and when the man is about to use his gun, Gibbs stabs him, killing him.
Gibbs often shows frustration with his team (particularly Di Nozzo for rambling or Mc Gee for getting sucked into technical rambling) by slapping them over the back of the head, an action that is later shared between team members and known as a "headslap" or "Gibbs-slap".