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Grisha Callen (Chris O'Donnell)
- Broken Pedestal: Is a bit upset with Hetty when he finds out he's just one of many agents she's recruited and trained from broken homes. He seems to forgive her though.
- But Not Too Foreign: Son of an ex-Russian Army officer imprisoned in a gulag camp in Siberia and a Romanian mother.
- Combat Pragmatist: As a contrast to his partner's more typical fighting style.
- Deadpan Snarker: To give just one example, Callen and Hetty are in a graveyard remembering the dead. Hetty remarks she wants to just be gone: no flowers on the grave, etc. Callen says it won't happen, because he hears Granger's going to have her stuffed.
- Family Extermination: The Comescu crime family wiped out his entire family as retribution for his OSS agent father assassinating the Comescu patriarch due to his Axis sympathies. It traumatized him so much that he had the memory of his mother assassinated in front of him as a child was suppressed for a long time even before he joined NCIS.
- Feuding Families: The almost 70 year old feud between Callen's family and the Comescu family is the reason why he is an orphan.
- The Ghost: In-Universe, he is known as this among JAG, an agent who can slip into almost any disguise but no one knows his actual identity, the only thing known about him being his last name "Callen." One corrupt JAG lawyer tries to use Kensi as a hostage to lure him out and he gets shot for his troubles.
- Heterosexual Life-Partners: With Sam.
- Honorary Uncle: Sam's son Aiden calls him "Uncle G" in S7E11, "Cancel Christmas".
- Last-Name Basis: At one point, Callen asks Hetty why she never calls him by his first name (though she usually calls most of the other agents by their last names, too). She responds, "It's not a name. It's a letter."
- Last of His Kind: Callen is apparently the only living member of his family, which a certain Eastern European crime family has been hellbent on wiping out.
- Married to the Job: Callen. It worries Hetty a lot.
- Mysterious Past: Hell, he doesn't even know his own first name.
- It's finally revealed to be Grisha in S7E16, "Matryoshka, Part 2".
- No Name Given: See Mysterious Past for more details.
- Omniglot: G can speak English, Arabic, French, German (Which some people says has an Austrian accent), Italian (With a Northern accent), Polish, Russian and Spanish. He says that he can speak Czech and Romanian. In "Allegiance", he can speak Turkish. But Sam chews him out for not speaking the right words. G retorts that he intended to call Deeks a scruffy rodent.
- One-Letter Name: Due to the paperwork with his full name on it getting lost by the foster system.
- Orphan's Ordeal: His time in foster care was rather rough.
- Parental Abandonment: His father is a question mark, and his mother was killed by the Comescus. As of Season 7, he's met his Disappeared Dad, though.
- Trauma-Induced Amnesia: Callen witnessed his mother's murder but suppressed the memory most of his life.
Sam Hanna (LL Cool J)
- Bald of Awesome: Awesome guy despite having a bald head.
- Big Brother Instinct: According to Nate, it's his biggest weakness: trying to protect everyone.
- Cultured Badass: Among other things, he's a trained sommelier.
- Cunning Linguist: If there's a foreign language the team needs, Sam probably has it.
- Famed in Story: He's a legend in the SEAL community. One of his brethren even says that he's "who SEALs want to be when they grow up".
- Fan Boy: keeps the complete run of Silver Surfer comics in a national security-grade safe, and is a big fan of Black Panther."Not just 'cause he was a brother who was richer than Tony Stark. T'Challa was a leader, he was a president, he was a superhero all at the same time. He was all about justice."
- Genius Bruiser: A former Navy SEAL and all around Scary Black Man. As previously mentioned he speaks three additional languages fluently and can handle himself in Farsi, and he has extensively studied sharia law and The Qur'an. (He was also a Junior Math Olympian as a child.) Justified: They don't let Dumb Muscle into the SEALs.
- Happily Married: Although it isn't brought up much, to the point where Kensi and Deeks were very surprised when he offhandedly brought it up while interrogating a suspect. Callen knew about them, though. Sadly, Michelle's death has ended this.
- Hero of Another Story: His time with the SEALs in various theaters from the Balkans to the Middle East.
- Heterosexual Life-Partners: With Callen ever since they worked in OSP for years.
- It's Personal: In cases involving SEALs. And his wife's death. And that one case where a girl is Buried Alive, as it brings back some very bad memories for him.
- Jack Bauer Interrogation Technique: Sam dabbles in threatening people with this. For obscure reasons, despite this being caught on camera, the confession that results is never questioned.
- Limited Wardrobe: His outfit of choice◊ seems to be long-sleeved, four-button Henley shirts in assorted solid colors.
- Living Emotional Crutch: For Callen. It's said that "his partnership is the only stable thing in his partner's life."
- Omniglot: Sam speaks native English with Arabic, Japanese and Spanish. He's familiar with Farsi, but he didn't speak the language for a long time. In "Allegiance", he can speak Korean. But G chews him out for not speaking the right words.
- Papa Wolf: When his son's Military School gets taken over by terrorists, he leads the charge to take them out.
- Parental Abandonment: At least to his kids. The only thing Sam doesn't like is that extended hours makes him miss out on his kids' lives like school graduation.
- Scary Black Man: He uses his height and musculature to intimidate when he's working or using an alias, and even with his coworkers, he carries a strong aura of "Do NOT mess with me."
- Stout Strength: He's not actually obese, but he's definitely not skinny. He is, however, a Lightning Bruiser in hand-to-hand combat.
Kensi Blye (Daniela Ruah)
- Action Girl: She's an experienced OSP agent who can stand on her own during fights.
- Disappeared Dad: He was murdered and his case was a cold case for years until it was solved in Season 3 episode "Blye, K Part 2".
- Eye Scream: To a degree. Kensi - and, of course, the actress - has an unusual birthmark on the white of one of her eyes which gives her a distinctive look (but otherwise has no effect on her vision). Viewers who might not be aware of this unusual trait might think that Kensi, or the actress, has some sort of eye injury or a completely dark eyeball depending on the lighting and camera angle. In reality, of course, neither is the case.
- Fair Cop: She's an attractive Field Agent in the NCIS.
- Friendly Sniper: She enjoys the usual camaraderie with her colleagues, has an "are they or aren't they" relationship with another agent, and often takes part in the show's humor. And the in the next scene she is cold-bloodedly sniping bad guys to death. She doesn't fit the "loner" aspect of the trope, but otherwise... shudder.
- Good Is Not Soft: A kind-hearted character, the subject of a longstanding ship pairing... with one of the highest body counts of any female character in network TV history. See also Friendly Sniper, above.
- Lad-ette: Views of her home are basically that of a bachelor pad.
- Light Feminine Dark Feminine: Downplayed. Dark to Nell's Light.
- Military Brat: Was born on U.S. Marine Corps family and was raised in military camps.
- Ms. Fanservice: Perhaps the inevitable result of being the only female regular under the age of 40 (until Nell came along, but Nell's not that sort of character), although she's fairly mild compared with some - but a lot stronger than Ziva David.
- Omniglot: She can speak English with Portuguese and Spanish. (In real life, Daniela can speak the last two languages fluently aside from English, which doubles as a The Cast Showoff). In "The Dragon and the Fairy", she displays her proficiency in French.
- Properly Paranoid: In "This Is What We Do", she gets antsy around Asakeem after he's used to draw out armed Islamists in LA. When she sees him trying to walk on the beach, she takes her sidearm out. Turns out that Asakeem is trying to pray to the direction of Mecca, as a requirement for all practicing Muslims.
- Red Oni, Blue Oni: Blue Oni to Deeks' Red.
- Semper Fi: she's a Marine brat.
- Tomboy and Girly Girl: The Tomboy to Nell's Girly Girl.
- Unresolved Sexual Tension: With Deeks. Season 5 resolved it. In Season 6 they do get together while ice-skating. As of the season 8 finale, they are engaged.
- Written-In Infirmity: Kensi is sent on an assignment to Afghanistan in Season 5 due to Daniela Ruah's pregnancy.
- Wrench Wench: She was an only child, so her father taught her everything he'd teach a son, including things like fixing a car and wiring a house.
- You Killed My Father: She goes after one of her father's colleagues in the Marines for getting him killed.
Nate "Doc" Getz (Peter Cambor)
- A Day in the Limelight: One episode has him contemplating becoming an agent and teaming up with Kensi temporarily. Everyone thinks he wouldn't make a good agent.
- Hidden Depths: Plays the harmonica.
- The Profiler: Nate does by providing exposition on suspects OSP investigates.
- Put on a Bus: At the start of season 2.
- Commuting on a Bus: Has returned several times: mid-season 2, once in season 3 and 4, twice in season 5 and once again in season 6. And again in Season 7.
- Took a Level in Badass: In season two, Nate goes away for an episode or two, comes back, and somehow picked up the ability to shoot. Everyone wonders what happened.
Dominic "Dom" Vail (Adam Jamal Craig)
- Black and Nerdy: He had his moments. His bobble-head was the best example.
- Butt-Monkey: As the new guy, Dom copped a lot of flak.
- Heroic Sacrifice: During the team's mission to save him, he steps in front of gunfire and is killed saving Sam.
- Killed Off for Real: In the Season 1 episode "Found".
- New Meat: A Police Procedural version of this.
Anna Kolchek (Bar Paly)
- Action Girl: Anna helped OSP solve several cases prior to being recruited by the US Marshals.
- But Not Too Foreign: A first-generation Russian-American who moved to Champaign, Illinois when she was young.
- Generation Xerox: Anna was in law enforcement like her father. Although unlike him (he was with the Soviet KGB), she joined the Chicago Police Department.
- Official Couple: As of Season 8, she's with Callen.
Marty Deeks (Eric Christian Olsen)
- Abusive Parents: His dad tried to shoot him at least twice. Or maybe once. The show is a little unclear about it.
- Afraid of Needles: He faints when Hetty gives him a shot in 3x21.
- Played more seriously in 5x1, after surviving torture via dentist drill and being taken to surgery, he sees a syringe and stares at it visibly terrified.
- All Take and No Give: Despite his Butt-Monkey tendencies, he would probably be this wasn't it for casual hints from the team that they do care... which become increasingly less casual.
- Ascended Extra: Got promoted from recurring character to principal cast in season 2.
- Berserk Button: A dirty cop once mocked a woman Deeks had a relationship with; a fellow cop that the dirty one had framed for his activities after she'd been killed by a crimelord. Deeks pulled his gun on the man, and after surrendering it to Sam, proceeded to beat the hell out of him with his bare hands.
- Beware the Silly Ones: Deeks uses his jokes to throw people off guard and get them to trust him. But when angered he can quickly turn deadly such as attacking a cop who made fun of his recently dead partner and torturning a blind cleric when Kensi is kidnapped.
- Butt-Monkey: As the newest on the team, G, Sam and his partner Kensi all tend to pick on him, though he tends to either shrug it off or play it up. In one or two tense episodes, it's implied he sets himself up for teasing to lighten the mood.
- The Charmer: Deeks is a trained undercover detective. He uses charm to get into places and get people to trust him so he can further get into the group.
- Chivalrous Pervert: For variable levels of chivalry and perversion. He also uses it to diffuse tension in certain situations.
- Deadpan Snarker: He often has a sarcastic joke to work in any situation.
- Distressed Dude: After being shot twice, kidnapped, used as bait, beat up on numerous occasions, and being involved in more explosions than this troper can count - honestly, the only person who MIGHT rival him is Callen, and that's only because he's the last surviving member of a family that's been feuding with another for decades and everybody wants to kill him.
- Though he may count, at times, as a Badass in Distress since he does tend to get himself out of those messes.
- Considering he saved Kensi's life by shooting the baddie before he could kidnap her after racing down a couple flights of stairs to get to her when he worked it out in his head that he was the bait to lure her out of hiding. And that was after he'd been shot. Twice.
- He also has been tortured by Siderov while being asked if Michelle was an agent.
- Though he may count, at times, as a Badass in Distress since he does tend to get himself out of those messes.
- Drama Queen: He is always freaking out in the worst times. Normally used for comical relief.
- Dude, Where's My Respect?: Up until Descent/Ascention Sam never trusted Deeks. But after Deeks is tortured and protects Michelle Sam grows to respect the detective.
- Friend to All Children: Seems to have a knack for bringing kids out of their shells.
- Heroic BSoD: Seems to be falling into this after being brutally tortured during the season 4 finale.
- Hidden Depths: Grew up playing the violin, and seems to be able to sing as well. Also, was a public defender before he became a cop. He also worked in Robbery for two years before becoming a Detective.
- Manchild: Deeks often speaks of watching cartoons and reading comics along with over-the-top whining. Though how much of this is real and how much is a front we don't know.
- Manic Pixie Dream Guy: A rare male example of this trope.
- Missing Mom: Up until season 7 his Mom was a mystery. In Personal we learn that she isn't put down as his next of kin prompting Hetty to be and yet in Citadel we meet her and they act like they have always been together. This has yet to be explained.
- Nice Guy: Every Christmas Eve, he volunteers at a soup kitchen.
- Obfuscating Stupidity: Deeks often pretends to be stupid or mishears things for comedic effect but really he's quite smart having both passed the bar and on cases he often can see things the others can't.
- Overshadowed by Awesome: If this show had been about the L.A.P.D., Deeks would have been The Hero. Next to G, Sam, and Kensi, however, he's The Chick.
- Real-Life Relative: Olsen is the RL brother-in-law of Daniela Ruah; she's married to his brother (who is also the stunt double for Deeks!)
- Red Oni, Blue Oni: Red to Kensi's Blue.
- Sixth Ranger After Dom is killed
- Standard Cop Backstory : He shot his father when he was 11. The last time Deeks saw him, his father tried to shoot him with a shotgun on Thanksgiving.
- Undercover Cop Reveal: The team first met him when he was at an MMA gym, posing as a fighter named Jason Wyler. Hetty revealed the truth halfway through.
- Unresolved Sexual Tension: With Kensi. Season 5 resolved it. In Season 6 they do get together while ice-skating. As of the season 8 finale, they are engaged.
- You Can Leave Your Hat On: Paid his way through law school and the Police Academy by stripping.
NCIS Support Personnel
Eric Beale (Barrett Foa)
- Adorkable: Very.
- Belligerent Sexual Tension: He and Nell can lapse into this when she feels he doesn't give her enough importance, or when they get competitive. It's mostly playful and benign.
- Closet Geek: A very, very transparent closet—one that embarrasses him occasionally around Nell. Varies between this and Proud to Be a Geek.
- Hollywood Hacking: Generally averted, occasionally played painfully straight.
- Mission Control: Helps the OSP team by providing details from the Ops office.
- Non-Action Guy: The one time he's forced into the field, he's terrified he'll have to carry a gun. Hetty gently informs him she wouldn't forgive herself for forcing him to carry a weapon, and he's happy to return to Ops when he's done.
- Preppy Name: He gives his full name as "Eric Bartholomew Beale III, Esq." in S 6 E 2, "Inelegant Heart".
- Took a Level in Badass: While out on field training with Kensi and Deeks, the suspect they're trying to arrest fires at them. Eric manages to neutralize said suspect by throwing a flash grenade.
- Unresolved Sexual Tension: With Nell. The 2012 Christmas Episode had them kissing under mistletoe.
Penelope "Nell" Jones (Renee Felice Smith)
- Badass in Distress: She's been taken hostage a few times. The first used her as a human shield so she unloaded his gun. The second manages to take her gun so she pulls a knife and stabs him repeatedly.
- Belligerent Sexual Tension: She and Eric lapse into this when she feels he doesn't give her enough attention, or when they become slightly competitive. It is mostly playful and benign.
- Beware the Nice Ones: Unlike Eric, she is field trained and carries a gun when in the field. She hasn't had to use it that often, but she has captured a few suspects and disarmed a trained opponent who had taken her hostage and was using her as a human shield.
- Cry Cute: Well almost. In "Free Ride", she almost went to this since Nell wants to spend the holidays with her family. Due to the case, she can't leave until it's solved.
- Girly Bruiser: Once escaped from a gunman holding her hostage. Callen also once nicknamed her "the Nellverine" after she took down two different fleeing suspects hand-to-hand in the same day.
- Hollywood Hacking: Generally averted, occasionally played painfully straight.
- Exposition: What she's commonly used for.
- The Lad-ette: According to a profile created for her by her sister. Subverted when it turns out that, among other things, she doesn't know anything about football.
- Number Two: Hetty appears to be training her as a potential successor.
- Sugar-and-Ice Personality: When forced to take Hetty's place, she reveals that she can become just as authoritative and efficient as her for routine work.
- Tomboy and Girly Girl: The Girly Girl to Kensi's Tomboy.
- Unresolved Sexual Tension: With Eric at times. She did kiss him at one point.
Henrietta "Hetty" Lange (Linda Hunt)
- And Starring: Hunt gets the 'With'.
- The Atoner: She has blamed herself for the deaths of several agents to a point that she has tried to resign. Three times. All she does is change the date on the letter.
- Badass Bureaucrat: Being a bureaucrat (and a diminutive one at that) doesn't make her any less badass. She used to be a field agent and she's proficient in many weapons, including some exotic ones.
- Badass in a Nice Suit: She prides herself on her haute couture. In one episode, where Abby Sciutto assists the team in taking down a serial killer, Hetty compliments Abby on her own unique sense of style.
- Catch Phrase: "Oh, bugger."
- The ChessmasterCallen: When are you gonna stop moving us around like chess pieces!?Hetty: I don't move pieces, Mr. Callen. I move the board.
- Guile Hero: She is once called The Duchess of Deception
- Hero of Another Story: Prior to joining NCIS, she participated in black ops missions to rescue American/Allied soldiers captured and held in Vietnam, even with the fall of Saigon in 1975.
- Mama Bear: Hetty does some long distance Mama Bearing when Sam and Callen are held hostage by militia she uses her "political capital" with the Secretary of the Air Force to send them backup in the form of fighter jets.
- The Mentor: To the LA team when they need her help or advice.
- My Greatest Failure: Failing to save Callen's mom. As well as the deaths of previous agents. Later on, she goes to Southeast Asia to investigate one of her old colleagues who is locked up by the current Vietnamese government, who she thought died in captivity after the Vietnam War.
- Mysterious Past: She could tell you, but she'd probably have to kill you.
- No Celebrities Were Harmed: Hetty, like a certain Edna Mode, is modeled after costume designer Edith Head. In "Imposters" she mentions to have worked with Bette Davis on Death on the Nile, so Hetty might actually be Edith Head in the NCIS universe.
- Not So Above It All: At the end of the street racing episode, Hetty spots Eric's Segway in the empty office. The last few seconds of the episode is her riding it, whooping.
- Not So Stoic: Snaps at Callen when he challenges her on recruiting and losing so many vulnerable agents. See his Broken Pedestal moment, above.
- Noodle Incident: Has many, often from the Expansion Pack Past being a Mysterious Past.
- She once ruled Nicaragua for 72 hours. "Don't ask."
- "Hetty, plus tequila, plus mechanical bull, equals bar fight."
- Omniglot: English and German and in "Allegiance", Welsh. Her personnel file in "Familia" lists her as also being fluent in Russian, Mandarin Chinese, Spanish, Czech, Romanian, Hebrew, Arabic, Hungarian, and Pashto (the primary Afghan language). The same file says she attended the Defense Language Institute (a DoD institute that teaches foreign languages to soldiers and federal agents), which is presumably where she learned most of these languages.
- Parental Substitute: To Callen. She's always had a special connection to him given their shared history.
- Parental Abandonment: Her parents died shortly after being freed from a Nazi concentration camp and she was adopted.
- Shrouded in Myth: Many of her schemes precede her.
- Team Mom: She is a mother figure to everyone under her care, and extremely protective of all of them.
- Took a Level in Kindness : Though she proved kind and caring since the pilot, she reached new levels in season 2 and 3.
Owen Granger (Miguel Ferrer)
- Bus Crash: Miguel Ferrer died from throat cancer in the middle of 2017, and the writers had been working out a way to address this by writing his terminal infirmity into the story. After trying not to rip the band-aid off his actor's passing by having his character depart in Season 8, the writers finally get around to the sad task of officially killing Owen off next season, off-screen. It's revealed he managed to reunite with his daughter while critically ill and dying from his cancer. After making his peace with her, he went off his medication that was sustaining his life, quietly and weakly made his way to a tall tree on top of a hill, sat down under it in the shade... and died peacefully. His daughter later buried him in that spot.
- Comically Serious
- Guile Hero: He prefers to manipulate targets into revealing something or tricking them into leading NCIS to something unwittingly.
- Hero of Another Story: Prior to joining NCIS, he participated in black ops missions to rescue American/Allied soldiers captured and held in Vietnam, even with the fall of Saigon in 1975.
- Jack Bauer Interrogation Technique: When a suspect working for a Private Military Contractor demands to speak with his lawyer, Granger hands him his phone and lets him dial. As the suspect raises the phone to his ear, Granger fires his pistol right next to the suspect's ear, then tells him the next bullet is going into his head unless he talks.
- Obstructive Bureaucrat: He has good reasons sometimes...
- Parental Substitute: Kensi saw Granger like a second father to her, and was even going to ask him to bring her down the aisle at her weeding. It's sad that he didn't last long enough nor stick around to see it happen.
- Real Life Writes the Plot: He goes rogue/off the grid after his actor passed away from throat cancer. And then after the cast and production crew's grief has subsided and they've had time to heal, his character is officially revealed to be dead and buried in the episode "Liabilities".
- Lethal Diagnosis: With respect to his actor's condition, Granger was diagnosed with throat cancer and told he had only a few months left at best. This implies that his character is destined to die off-screen. And in Season 9, we learn he did.
- The Patient Has Left the Building: The manner in which Owen is posthumously written out of the show, said to have suddenly flown the hospital without warning, leaving a goodbye note to Hetty indicating he will not be coming back.
- Reasonable Authority Figure: ...and has been very accommodating to the team the more he works with them.
- Team Dad: It shows in season 6, as while Hetty is Hauled Before A Senate Subcommittee, Granger is helping the team avoid the Department of Justice investigators. Later on in the season, also, when he tries Deeks's Swedish nachos.
- Later exemplified when Kensi reveals that because she lost her dad, she wanted Grainger to walk her down the aisle in his place on the day she eventually got married... except by that point, he parted ways with the group. And due to his actor's sudden passing, we know he won't be coming back.
- Was It Really Worth It?: He's had to do a lot of Dirty Business over the years. After Fatima Khan (a woman he saved as a child) tried to kill him and Hetty for planting a car bomb that killed her father, he's left seriously wondering if every mission they performed was worth the costs.
Harley Hidoko (Andrea Bordeaux)The executive assistant to new NCIS Executive Director for Pacific Operations after Hetty resigns. Like Nell, she sometimes joins the others in field operations.
- Action Girl: Like Nell, she helps the OSP team on raids when manpower is needed.
- Dark Secret: She's actually a widow who never even got to experience a full day with her husband, as they performed a wedding ceremony while he was dying.
- Uncertain Doom: The finale of Season 9 sees Hidoko eerily disappear after going off to Mexico. From our point of view, some unidentified person is violently murdered and incinerated near the beginning of the episode. The agents Never Found the Body, but did find evidence that someone had been burned to oblivion, hoping that it wasn't her. And now it turns out that it was her.
- Widowed at the Wedding: Married a fatally wounded soldier in Afghanistan just to give him the benefit of being wed to her out of love.
Shay MoselyThe new NCIS Executive Director for Pacific Operations. She used to be with the Secret Service.
- Hero of Another Story: Her work with Secret Service prior to her NCIS recruitment.
- Reasonable Authority Figure: Not at first, she sometimes gets into disbelief about ludicrous requirements such as conducting false flags op to deceive suspects and getting high-end cars for sting ops.
- Shay: I should have stayed in D.C.
- Took a Level in Jerkass: Her actions in the Season 9 finale are firmly rooted in a vicious Mama Bear state of mind and she becomes an absolute terror and relentlessly abuses her authority over the rest of the team.
John RogersA Special Prosecutor sent to assess the OSP team in the wake of the events in the 9th season.
- Fire-Forged Friends: With the team. He starts out with a seemingly hostile investigation (to which the team responds by being as uncooperative as possible), but it's understandable given the epic cock-up that he's investigating. Once the team is cleared, his working relationship with them greatly improves.
Louis Ochoa (Esai Morales)The NCIS Deputy Director who oversees the OSP after Mosely's departure.
- Reasonable Authority Figure: He knows how much leeway to give the team in order to get things done, and he genuinely admires them for their successes.
Fatima NamaziA Special Agent brought in to support the OSP team.
Mike Renko (Brian Avers)
Lara Macy (Louise Lombard)
- Chuck Cunningham Syndrome / The Pete Best: She only appears in the NCIS 2-parter "Legend". Hetty was added to the team in her place.
- Bus Crash: Killed off a year later in the parent show.
- Screw the Rules, I Have Connections!: How she gets around LA's social life since she's a known insurance broker. Plus, some of her insurance cases connect to active NCIS cases.
Isaak Sidorov (Timothy V. Murphy)A former Russian FSB agent turned ruthless arms dealer. He gets on the radar when he steals at least three nuclear bombs. He apparently has a long history with Quinn, whom is, unbeknownst to him, Michelle Hanna, Sams wife.
- Arms Dealer: The "Former Reds With Rockets For Sale" type. His role in the plot starts when he attacks a group of Russian sleeper agents that were hiding nuclear bombs. The reason? To sell the bombs for a profit.
- Ax-Crazy: Quinn points out that her clients aren't usually as happy to see her as him. His response? "They don't enjoy killing as much as I do." It's implied he killed his current girlfriend simply because she was jealous of Quinn.
- Big Bad: Of Season 4, as his plans to sell a nuclear warhead consume much of the team's efforts. Though it becomes a Big Bad Ensemble with Marcel Janvier after the latter re-enters the field.
- The Chessmaster: By the time the NCIS team goes after him, he's already gotten his hands on at least three nukes.
- Cold-Blooded Torture: He used it to find the nukes. In the Season 4 finale, he captures Sam and Deeks and uses Electric Torture and a dentist drill on them, respectively.
- The Dreaded: Just the mere mention of his name is enough to make any conversation tense. Even The Mafiya is terrified of him.
- Killed Off for Real: In "Ascension", Sam shoots him up real good.
Marcel Janvier (The Chameleon)
- Arch-Enemy: For the team in general and Agent Callen in particular.
- Asshole Victim: Suffers various severe injuries throughout the show. No-one feels sorry for him.
- Ax-Crazy: Has absolutely no concern for other's life and is possibly the most psychotic villain in the show.
- Beneath Suspicion: Invokes this trope. When he's on a job, he often passes himself off as someone low on the totem pole, like a mere driver. He generally uses a frontman to make the deals for him.
- Big Bad: Of the finale of Season 3 and the premier of Season 4. He later elevates himself to Big Bad Ensemble of the finale of Season 4 and premier of Season 5 with Isaak Sidorov.
- Body Horror: First, he is shot in the face by Callen. Then has one of his hands cut off by Vaziri.
- Boxed Crook: At the end of Season 4, Callen "recruits" him to lure Sidorov into revealing the location of his stolen nukes. Janvier seems to play along, but then he exposes Sam and later, slips the leash.
- The Chessmaster: Single-handedly manipulates NCIS multiple times into doing what he wants, including wiping out a family of arms dealers, manipulates Sam, Kensi and Deeks to almost getting blown up all to get his revenge and screw with Callen. He also likens his actions to a game of Chess.
- Covert Pervert: Implied in his debut episode to have a liking to women with tattoos. Whether this is true or not is never confirmed.
- Cruel Mercy: Is on the receiving end of this from Callen at the end of "Ascension". Callen even makes sure to be there when he's sent to jail.
- Death Seeker: When he appears in "Descent" he asks Callen to kill him. He subsequently tries to provoke Callen into doing so. It fails.
- Faux Affably Evil: Will act incredibly polite towards you while describing how he will kill you. He also regularly sends Callen a Christmas card, which Callen places next to a picture of himself and Joelle with Sam and Michelle.
- Hero Killer: Responsible for the deaths of both Lauren Hunter and Mike Renko. He's also responsible for Sam and Deeks getting tortured by Sidorov
- Hired Guns: Although he sometimes appears to have a gang, the Chameleon just hires (and disposes of) people as needed.
- Master of Disguise: Played with. While he doesn't impersonate anyone himself, he can fake being a variety of nationalities. He's also very good at passing himself off as Beneath Suspicion.
- Refuge in Audacity: In his first appearance, he arranges the death of the Interpol agent tracking him. He then hires a guy to contact NCIS and impersonate the agent.
- Roaring Rampage of Revenge: Although he didn't start out this way, when he enters the show his entire reason for living is literally to get revenge on Callen for shooting him in the face. It isn't just Callen either; during "Ascension" he goes after the guy who cut off his hand and pays him back twice over.
- The Sociopath: Marcel Janvier cares only about his own profit and has no regard for human life.
- Xanatos Speed Chess: In the Season 5 premier, during his escape from Callen, Marcel constantly updates his strategy to the point of cutting off parts of his own skin just to get rid of the tracking residue Callen placed on him.
- Arch-Enemy: For Sam after his time in Sudan.
- Big Bad: Of Season 7, and the finale of Season 8.
- Hero Killer: Masterminded the op that led to Michelle Hanna's death in Season 8.
- Hoist by His Own Petard: Gets killed by his own IED after Sam escapes.
- It's Personal: Sam earned his undying hatred for making Tahir's sister turn on him, leading Tahir to target Sam's family in turn, which made it personal on both ends. After kidnapping and killing Michelle Hanna, the rest of the team all want him dead.