- Death by Origin Story: It was their deaths that made Gibbs into the agent he is today.
- Dramatic Irony: Had Gibbs not taken the career path that led to their deaths, he would have died instead.
- Kill the Cutie: Both were murdered by a drug cartel leader while Gibbs was trying to hunt him down. He killed the NCIS agent driving their vehicle, causing the vehicle to wreck, and the crash slew both of them.
- Love at First Sight: Gibbs spotted her in a store window, the two shared a sweet look, and then by happenstance met at the train station waiting for the same train, chatted it up, decided to ride the train together, and that was that.
- Posthumous Characters: They still show up much in the same way Gibbs internalizes Mike Franks.
- She Knows Too Much: Shannon wanted to testify against Pedro Hernandez and his drug cartel. This got her and Kelly assassinated.
- Small Role, Big Impact: Shannon is the originator of Gibbs's rules to live by as an agent, having originally started them for herself in a more lighthearted manner. For instance, "Never date a lumberjack" makes more sense coming from her than a male. Gibbs then incorporated them for himself.
- Actor Existence Failure: Ralph Waite passed away in February 2014. The season 11 finale became an episode in his honour, with his character dying after suffering from a stroke.
- Cool Old Guy: Though technically, he isn't a grandfather anymore, he's still old and badass.
- Dad the Veteran: He served in WWII as a fighter pilot.
- Death Glare: Tony described him as "the only one who could do the "Gibbs Stare" at Gibbs."
- Like Father, Like Son: When Paloma Reynosa comes to kill him in "The Spider and the Fly".Reynosa: But we have so much to talk about.Jackson Gibbs: From what I hear, you didn't come to talk. (pulls his shotgun)Reynosa: You are just like your son.Jackson Gibbs: No, ma'am. He's just like me.
- Parent with New Paramour: The root cause of Gibbs' estrangement with his father was that his father showed up to the funeral of Shannon and Kelly with a date (which ultimately didn't work out).
- "Well Done, Dad!" Guy: Jethro blamed him for losing his mother. Their relationship has been slowly healing.
- Abusive Parents: Ann and Jackson were constantly bickering and implied to have even been skipping out on each other when Gibbs was growing up, because Ann felt a sense of dissatisfaction with the way things turned out living in Charlottesville. Her alienation of affection also caused him to lose face because he was implied to be schmoozing up other women outside the marriage. She finally walked out on the family, and Jackson feels like he ultimately failed to make Ann happy and let her down. Gibbs also notes his dad hated that she left him.
- Dead Person Conversation: Gibbs meets her as one of the many deceased friends and loved ones who visit him in the diner in "Life Before His Eyes".
- Deceased Parents Are the Best: Zig-zagged; she was no award-winning wife, that's for sure, but putting chocolate syrup on her son's waffles shows how much she loved her son as a mother.
- Despair Event Horizon: Her cancer diagnosis made her give up all hope of happiness and prompted her to take her life while she had all her faculties intact.
- Driven to Suicide: Killed herself by overdosing on pills to avoid a slow and painful death and making her family watch her slowly wither away.
- Fiery Redhead: She is obviously the reason why Gibbs favors redheads- they remind him of his mother.
- Karmic Death: After she split from Jackson, terminal cancer befell Ann. She took fate into her own hands and ended her life before she became sickly.
- Lethal Diagnosis: Following her separation from her husband, perhaps as a result of all the pent up toxic emotions she had from the failed marriage, her body withered and developed a killer form of cancer.
- My Greatest Failure: Her apparition in "Life Before His Eyes" tells Gibbs that she's aware she gave his father nothing but hell and helped to break apart the family because of it.
- Never Got to Say Goodbye: Poor Gibbs was just a boy when he lost Ann, and because of the sudden way Ann decided to go out, he was deprived of a chance to tell her how much she meant to him.
- Posthumous Character: Ann has been gone for a very long time, but she plays a big role in "Life Before His Eyes" and has a few appearances in flashbacks.
- Your Days Are Numbered: She was diagnosed with a terminal cancer.
Tony's father, a failed entrepreneur who likes to live large and has always been a distant and disappointing father to Tony.
- Breakout Character: He's popular enough to keep making appearances on the show even after his son has retired from NCIS (and moved to Paris).
- Chivalrous Pervert: He turns the charm up to eleven whenever there's a woman present (and apparently has had a long string of lovers) but is always polite and never untoward anyone. Ziva and Abby like him and flirt right back, which is saying something.
- Con Man: Junior thought that Senior was one for most of his life. While it's true that Senior's been using his charms to mooch off of friends and acquaintances, Senior assures his son that he goes into his various ventures with pure intentions and tries to make an honest profit for himself and his investors but hasn't had the best of luck in the past several decades.
- Cool Old Guy: Much younger people hang onto his every word and he's always willing to impart advice (although it's usually something superficial that sounds deep) to them.
- Disappeared Dad: He and Tony were never close to start out with but a decades-long rift formed after the death of Tony's mother as both retreated within themselves to deal with the grief. Senior didn't help matters by shipping Tony off to boarding schools and abandoning him in hotels during vacations.
- Hidden Depths: Once managed to knock out a weapon dealer's bodyguard with one punch to the face. In his later years wanted to find a purpose in his life, and started to aid a homeless shelter's inhabitants with his connections and apparent wealth, such as giving one guy a brand new pair of shoes.
- The Load: At least, this is what Junior's attitude towards him often is — whenever Senior blows into town, he tends to drag Junior into all sorts of unwanted situations.
- Lovable Rogue: He's a wheeler dealer who oozes charm. Only Junior and Gibbs look at him with wary eyes and, even then, it's only to make sure Senior doesn't get into too much trouble.
- Like Father, Like Son: It's pretty obvious where Junior got his personality from.
- Mock Millionaire: He is a formerly wealthy businessman, who is trying to keep up the appearance that he is still wealthy. He's been broke several times already.
- Parent with New Paramour: For a while, Senior almost netted himself a recently-widowed friend with a daughter of her own and planned to marry her- and neither child minded the idea of becoming stepsiblings. But then she dumped him and Tony Junior found dear old dad loafing around his house in his pajamas and playing his breakup mix.
- Silver Fox: Has the knack for charming any woman he crosses.
- Wacky Parent, Serious Child: Shares this dynamic with Junior. Given how much of a goofball Junior can be, that's saying something.
Leon's wife, who is somewhat exasperated with the hours he has to work and the toll it has taken on their personal lives.
- Dropped a Bridge on Her: Critically wounded by Ilan Bodnar in Season 10, then died in surgery.
- Happily Married: To Leon.
- Sassy Black Woman: Downplayed.
Offhandedly mentioned (but not by name) as Kate's sister in Miami in season one, Cranston managed to get assigned psych eval duty on Gibbs' team just so she could meet Kate's coworkers. She appears in season eight.
- Affectionate Nickname: Tony refers to her as "Dr. Kate's Sister".
- Chekhov's Gunman: Kate casually mentioned her in a season 1 episode.
- The Ghost: She used to be that one character only mentioned in conversation. Until Kate is suddenly murdered, and has trouble dealing with closure, at which point she fully appears to conduct psych evaluations on the team and learn more about what happened to Kate and make peace with it.
McGee's sister. Asks for his off-book help when she finds herself accused of murder. Returns later as an offstage character during McGee's father's funeral.
- Sarah: But he loves NCIS...Gibbs: Evidently he loves you more.
- Big Brother Worship: When it looks like she might have killed a man, she goes to her big brother for help.
- Clear My Name: McGee helps her do this re the aforementioned killing.
- Distressed Damsel: In addition to the killing that she actually didn't do, she was also drugged and set up to be raped.
- Intelligence Equals Isolation: When she is upset she goes to a stray corner of the library to cry.
- Nerds Are Sexy: She is a great book lover and a great looker.
- Dating What Daddy Hates: Breena's father initially doesn't think much of Palmer and believes she can do much better.
- Happily Married: With Jimmy starting in season 10.
- Ugly Guy, Hot Wife: Downplayed; Jimmy's cute, but somewhat gawky, and described as an "autopsy gremlin" and his wife is bang-up beautiful to such a degree the others wonder how someone like Jimmy managed to land a total fox like her.
Bishop's husband. He works as an attorney for the National Security Agency. He also does the near-impossible by becoming actual friends with Gibbs, to the point where they have a biweekly racquetball match and chat on the phone almost daily.
- Adorkable: Abby outright calls him "adorable". Then there's his glasses and his school girl-like gushing over Gibbs and the team. He later seems similarly awestruck at Ellie's efficiency.
- Derailing Love Interests: Starts out as an adoring, loving, supporting husband to Ellie and clearly becomes even more enamored of her after seeing her in action in "Grounded". But within a year, after some smaller disagreements about his inability to share information about his job with Bishop, he admits that he's been having an affair with a coworker.
- Disposable Woman: A non-lethal version. Goes from loving husband to cheating SOB so fast one wonders if this was the writers' plan all along to get Ellie started on having the same tragic love life nearly everyone else does.
- Happily Married: He and Bishop were very much in love, but their jobs caused some tension. When they both worked at NSA, they could freely talk about their days but when Bishop moved to NCIS, Jake became legally prohibited from divulging anything about his work to his own wife so all they could talk about are the murders Bishop investigates. With this, the marriage became increasingly strained, with his workplace affair putting the final nail in the coffin, and they are now divorced.
- Hello, Attorney!: He's played by Jamie Bamber, so natch.
- Retcon: Bishop originally said that she and Jake knew each other in college, but Jake tells a story where they first met at the NSA.
- The Unseen: He spent a season and a half only being mentioned in passing or unheard on the other end of phone calls with Bishop before he made an appearance on the show. He did manage to help NCIS from afar by getting Bishop and Tony a NSA satellite feed when Gibbs and McGee were shot down in Russia.
- We Used to Be Friends: He was on good terms with Gibbs' Team, but all friendliness towards him went out the window once the affair came to light.
- Your Cheating Heart: Has an affair with a coworker at the NSA after Bishop joins NCIS. Bishop does not take it well, and all her teammates take her side in the matter.
McGee's Love Interest starting from late season 10 to the present; the two of them get married at the end of Season 14. She works for the Department of Defense and helps Team Gibbs during their interagency cases from time to time. In Season 15, she gives birth to Johnny and Morgan McGee.
- Beware the Nice Ones: She's a really sweet person, but you don't want to be on her bad side.
- Brainy Brunette: She's the senior intelligence analyst at the DOD.
- Disabled Love Interest: She and McGee began dating before the bombing that paralyzed Delilah from the waist down, and a main factor in their continuing relationship was both of them coming to terms with what had happened. They marry at the end of Season 14.
- Disabled Snarker: Delilah can get pretty snarky in certain situations. For example, when she and Abby call Tim letting them know that the twins are on their way and he needs to meet them at the hospital:McGee: How did this happen? I mean, you're not due for another three weeks.
Delilah: Well, apparently, the babies had other plans, darling.
- Handicapped Badass: After getting caught in a bomb blast in "Kill Chain", she is confined to a wheelchair while slowly recovering from her injuries. Nonetheless, that doesn't stop her from wanting to try skydiving. Or even going undercover.
- Happily Married: To McGee as of the end of Season 14.
- Nice Girl: The first for McGee. One of his first love interests tried to kill him.
- Official Couple: With McGee.
Delilah and Timothy McGee's twin son and daughter, who were born during Season 15's "Ready Or Not".
- Alliterative Name: Morgan McGee.
- Blue Boy Pink Girl: During their appearances, Johnny is clad in blue while Morgan is clad in pink.
- Dead Guy Junior: This is how both of them got their names. Johnny was named after his paternal grandfather, who died from cancer three years before he and his sister were born. Morgan was named after a security guard her father bonded with who was killed by a terrorist the same day the twins were born.
- The Ghost: So far, they've only appeared on-screen in person in the episode they were born. Since then, their on-screen appearances have been regulated to the photos their father has of them.
- Half-Identical Twins: Appearance-wise, both of them have brown hair and greyish eyes. Them currently having the same body type is justified by the fact that they're both young children.
- Polar Opposite Twins: According to McGee, Johnny is more of a sleeper while Morgan is "non-stop active".
- Unto Us a Son and Daughter Are Born: They are fraternal twins who were born during Season 15.
The daughter of Ziva David and Tony DiNozzo.
The adopted brother of Abby Sciuto, first appears in Season 13 "Sister City" and the Crossover episode of the same name on NCIS: New Orleans. The One with... whom she grew up, not the long-lost biological one.
- All-Loving Hero: In order to help Eva, the Russian spy, he obstructs the New Orleans team by setting ablaze an oyster bar.
- Good Is Dumb: He trusts everyone except for the two agency branches who are trying to protect him. He initially feared that he killed the victims on the plane with food poisoning.
- The Pollyanna: He has ridiculously good faith in people.
- Descent into Addiction: The Season 16 finale opens with her having suffered an overdose. Everyone assumes her drink was spiked until it's revealed that she's been using opioids for some time. She finally breaks down at the end of the episode and admits she needs help.
- Fiery Redhead: She really takes after her mother.