That's M. Allison Hart(:

Margaret Allison Hart, portrayed by Rena Sofer, is an attorney. She was contacted by Colonel Merton Bell while he was being tried by the Mexican authorities for bounty hunting in their country. Hart successfully got Bell released from prison on the condition that he not leave Mexico. Vengeful against the man who had sent him to prison, Bell sent Hart to Washington to defend any accused who were involved in Gibbs's investigations. Hart started to take up every case that involved Gibbs. Hart's skills as a lawyer were a match for Gibbs's skills as an investigator. Despite their animosity, they appear to be smitten by one another. It is even implied that they shared a kiss at the end of one episode. When Gibbs's former mother-in-law becomes a suspect in a murder investigation, Gibbs covertly hires Hart to defend her. He purposely makes mistakes in legal judgment to prevent her arrest, permitting Hart to get her out of NCIS's custody. In the episode "Patriot Down", Abby writes a report on the murder of Mexican drug dealer Pedro Hernandez, a crime committed by Gibbs in 1991 in retaliation for Hernandez's murder of his wife and daughter. The report never makes it to Mexico as it is intercepted by Hart, indicating that she has switched her allegiances.

That's Hollis Mann(:

Hollis Mann, portrayed by Susanna Thompson, first appeared in the episode "Sandblast". Lieutenant Colonel Mann is assigned by the Army CID to help in a co-operative investigation with NCIS involving a bombing at the Army-Navy Golf Club. She is offered a position at NCIS by Director Shepard, but instead chooses retirement, in the episode "In The Dark". She and Gibbs had a serious relationship, even earning the nickname "future ex wife number four" from Tony Dinozzo. Their attraction becomes overt in the episode "Sharif Returns", as they discuss their possible relationship but refuse to act on it until Sharif is caught. At the end of the episode, they kiss. Although she and Gibbs clearly have serious feelings for each other, she is often frustrated by his reluctance to express his emotions. In the episode "In the Dark", she returns from choosing her successor and confronts Gibbs, saying, "I'm aware there are three billion men in the world, and not all of them have to want me, but you should want me, and the fact that you don't makes me wonder why I ever wanted you." She is upset to hear that he has worked through the night to fix her plumbing, seeing it as a sign that he doesn't want to stick around. He calmly informs her that he did so because he wanted to surprise her, but that "it's gonna be a bigger job than he thought ... it's gonna take a while". She realizes that this is his oblique way of committing to their relationship for the long haul and kisses him fiercely. She last appears in the episode "Ex-File"; the relationship ends when she discovers that, no matter how strongly Gibbs feels about her, he is still mourning his wife and daughter. In the episode "Lost and Found", the "Stars and Stripes" military newspaper Shepard is reading reveals that she has relocated to the Hawaiian island of Lanai.

That's Holly Snow(:

Holly Snow (played by Dina Meyer) is a former Washington Madam. She has been in two episodes to date: "Jet Lag" and "Guilty Pleasure". In Guilty Pleasure Holly is found by Gibbs to be giving a seminar on sexual harassment in the work place, part of a plea deal she worked out after her last episode. Gibbs asks for her help tracking down a prostitute that is the common link to all his murder victims. Later in the episode Holly whispers a request into Gibbs' ear for her assistance. Gibbs declares that her request is "a deal breaker" but Holly states that the deal is the only way she will help his investigation. The killer ends up kidnapping Holly, blaming her for getting the prostitute into her lifestyle. However, she is saved by Gibbs before the killer can harm her. The episode ends with Gibbs and Holly having a simple dinner together as part of their deal. During which Holly receives a phone call and leaves dinner early, under the impression that she is meeting a John for business.