BEWARE OF SPOILERS! To prevent the page from being whited out entirely, only spoilers from the final season (5) are whited out!
Nathan C. Ingram
Introduced in: "Ghosts"
The co-creator of the Machine along with Harold Finch, and the founder of IFT.
- The Alcoholic: As his marriage falls apart and he becomes more disillusioned by his work, Ingram falls into alcoholism.
- Break the Cutie: When we first meet him, he's a carefree, happy-go-lucky sort of guy with a heroic streak. That was in 2002. By 2010, he's had an affair, divorced from his wife, haunted by the Irrelevant Numbers, his and Finch's friendship is being driven apart by their disagreement over the Irrelevant List, and he's become an alcoholic.
- Big Good: Filled this role before The Machine did. He decided to start trying to save the numbers way before John Reese took up his position at Team Machine, even when Harold disagreed and actively opposed him and set up the basic original infrastructure for Team Machine to utilize, i.e. the Library.
- Broken Ace: A charming man and an award winning software engineer but also plagued with a drinking problem and a conscience.
- The Charmer: Was shown to have this talent.
- Chronic Hero Syndrome: Haunted by the Irrelevant List, he sought out to stop what was going to happen to them. Some he saved. Others he didn't.
- Death by Origin Story: His (preventable) death was the catalyst that started Finch on his obsession with saving the Irrelevant Numbers.
- Deadpan Snarker: Especially around Harold.
- Expy: Of Steve Jobs, according to the casting call.
- Heterosexual Life-Partners: With Finch.
- Honor Before Reason: He wanted to go public about The Machine because he felt it was the right thing to do, and wouldn't listen to Finch when Finch said he thought that the government was killing off people connected with The Machine.
- Make It Look Like an Accident: Nathan's death makes it look like he's just collateral damage of a terrorist attack.
- The McCoy: To Finch's Spock (before his death and Finch's subsequent becoming something of a McCoy/Spock hybrid.)
- Only Friend: To all appearances, Ingram was Finch's only friend.
- Posthumous Character: Is dead when the series starts, and is only seen in flashbacks.
- Sharp-Dressed Man: He is almost always in a nice suit, in and out of the office.
- Suspiciously Similar Substitute: He's this to John Reese without the military experience. Both were Finch's Only Friend, have ruined personal lives and were the ones putting their lives on the line to try save the Irrelevant numbers.
- Talker and Doer: The talker and face of his and Finch's company.
- Too Good for This Sinful Earth
- What the Hell, Hero?: Gives one to Finch in a flashback, which forms part of the reason Finch ends up recruiting Reese to track the 'irrelevant' numbers.
- What You Are in the Dark: A guy who wants to help, with no plan, no backup, and no weapon worth a damn.
- Wide-Eyed Idealist: In contrast to Harold's cynical personality and initial willingness to let the numbers on the irrelevant list die, Nathan believed he could make a difference by saving them from their fate and coded the Contingency so the irrelevant list would come to him even after the Machine was black boxed.
- Your Cheating Heart: Though still married, he was carrying on an affair with a graduate student until The Machine exposed it to Harold.
A "fixer" and the occasional lover of John Reese. They meet when Reese and Finch helped saved her when The Machine gave them her number. She returns the favor by helping them out from time-to-time with persons of interest cases that require her particular skills.
- Action Girl: She has no qualms about getting into physical fights or infiltrating buildings, but would rather leave the violence to people with better skills than her such as John.
- Cool Car: She has a sweet Audi RS7.
- Dating Catwoman: Her relationship with Reese has shades of this.
- Deadpan Snarker: And How! Her temporary marriage to John was a glorious example of this.
- Femme Fatale: Especially around John; she flirts shamelessly with him and is certainly morally dubious...but she's a good person at heart.
- The Fixer: Her job.
- Friends with Benefits: Her relationship with Reese turns out to be this.
- Guest-Star Party Member: The most frequent ally of Team Machine that isn't a full-time member. Finch often calls on her aid when dealing with PO Is that have political connections/motivations.
- Guile Heroine: Qualifies due to her stalling of the murderous pharmaceutical executive and counting on John to break out of his handcuffs with the paper clip she slipped him and get to her in time.
- Hero of Another Story: Appears a couple of times when her own job just happens to intersect with Team Machine, but they're not Working the Same Case. In one episode, she steps into a hotel lift to find Reese dressed as a bellhop. Both are too professional to insist on explanations; they just enjoy the encounter.
- Honorary True Companion: Though she is trusted as much as Carter and Fusco, she always returns to her job after helping Team Machine out.
- I Was Never Here: In "Bury the Lede":"It was a pleasure meeting you, but it's a shame we never met."
- Lady in Red: As befits her Femme Fatale nature, she's oft seen in a red overcoat.
- Nerves of Steel: Extremely so. Very few situations can make Zoe flinch.
- Only in It for the Money: How she presents herself to the world; it seems she actually has a Hidden Heart of Gold.
- Put on a Bus: As Paige Tuco has signed up to NCIS New Orleans, it is unlikely we will see her for some time.
- Ship Tease: With Reese just about every time they're on screen together. Seemed to have been elevated to Love Interest as of "Booked Solid"; confirmed in "Lady Killer."Shaw: I clocked you and Zoe right off the bat...
- The Social Expert: As a fixer, her job is to understand human interactions to allow her how best to handle some situations.
Grace R. Hendricks
Harold Finch's fiancée, who believes he is dead. She still lives in New York, working as an illustrator. Although Finch is unable to see her, he will still occasionally sit in Washington Square Park, near her home, using an app that alerts him in case he ever gets closer than hundred meters around her.
- Birds of a Feather: She and Finch are both quiet, thoughtful, inwardly intense people, who love books and art and are kind despite the suffering they've gone through.
- Bookworm: Holds a deep love for Charles Dickens.
- Casting Gag: The character's actress, Carrie Preston, is Michael Emerson's (Finch) real-life wife.
- Dark and Troubled Past: Her father was an emotionally abusive alcoholic.
- Geeky Turn-On: She had this when she found out Finch has an enthusiasm for the art of Giorgio de Chirico, the artist whose works inspired her to be an artist.
- Girl Next Door: Gives off this sort of vibe.
- Heroes Want Redheads: Yep, she's a redhead.
- I Have Your Wife: Is targeted by Decima as a way of getting to Harold.
- Meaningful First Name: Just look at her name and the character quote.
- No, Mr. Bond, I Expect You to Dine: Greer offers her a Spot of Tea as his captive. She pointedly refuses.
- Plucky Girl: She's been through the wringer, but she's determined that she won't let the world break her or make her bitter.
- Put on a Bus: After being kidnapped by Decima to get to him, Harold arranges for her to get a well-paying job under a different identity in Italy.
- Satellite Love Interest: Every time she's brought into the show, it's to emphasize her relationship with Harold.
- Shut Up, Hannibal!: Marvelously gives one to Greer:"I don't know who you are or how this ends, but we're done here."
- Single Woman Seeks Good Man: She was this for a time.
- Starving Artist: Averted. Her illustration and creation of cover art for magazines is steady enough to keep her living comfortably. Though Finch keeps an eye on her and makes sure someone hires her if no one has hired her for a while.
- The Mourning After: Harold still is her fiancé, his "death" in 2010 notwithstanding, and she has trouble referring to him in past tense.
- Villain Over for Dinner: Root invited her for coffee in order to threaten her safety to get Finch to do as she wants.
- You Can Always Tell a Liar: Because of having to deal with an emotionally abusive and manipulative father, she is good at picking up tells for whether someone is trustworthy.
Reese's deceased lover. After Jessica's relationship with Reese ended, she married another man, but remained in contact with Reese. She is eventually killed by her husband during a domestic dispute.
- Accidental Murder: A victim of this.
- Character Death: She's killed by her abusive husband.
- Domestic Abuse: The man she chose after Reese left her was not the nicest of men. He caused her death.
- I Will Wait for You: She offers to wait until Reese comes back from the war, but he refuses, thinking she should find a better man than him.
- The Lost Lenore: With respect to Reese.
- One Degree of Separation: Turns out she was also one of the people on the Irrelevant List that Harold and Nathan failed to save.
- Posthumous Character: Dead before episode 1.
- Satellite Love Interest: She is a Posthumous Character whose only relation with the cast is through John.
Introduced in: "The Contingency"
Reese: We don't pay you anything, Leon.
A former forensic accountant and three-time Person of Interest. He is targeted to die by the Aryan Nation, the Russian Mafia and Nigerian fraudsters and is always saved by the timely intervention of Reese and Finch. He returns the favor by helping them out with persons of interest that require his skills.
- Asian and Nerdy: It doesn't get more stereotypical than being Chinese and an Accountant.
- Butt-Monkey: Tends to have bad things happen to him, such as getting in the List three times.
- Did Not Get the Girl: He's pretty upset over it too, despite the fact that she was being paid to help kill him.
- Forensic Accounting: Extremely good at it, picking apart the motivations for the conspiracy to kill the energy company owner in "Critical."
- The Friend Nobody Likes: Neither Reese or Finch are particularly fond of him, though mainly due to his Too Dumb to Live tendencies causing them to repeatedly have to save him. Several times in season 2 see them forced to call on his aid, though, either because the latest Person of Interest requires his particular skill set or because Carter and Fusco are unavailable to provide another body.
- Genre Savvy: By his final appearance, he's started to predict the timing of Reese's Big Damn Heroes moments. He even tells the thugs that are trying to kill him to make a run for it before they get beaten up.
- Guest-Star Party Member: In "Critical", "Relevance", and "All In", he helps Team Machine with the latest number. The first time wasn't voluntary (he just happened to be at Finch's library due to being the previous number), but the latter two are.
- Honorary True Companion: Despite his general stupidity, he is quite loyal to Team Machine. So much so that they even trust him to save Shaw from Northern Lights.
- Pay Evil unto Evil: Loves stealing money from criminals (e.g. Aryan gangsters, Nigerian scammers, etc.), even though it keeps getting him into trouble.
- Plucky Comic Relief: Almost every scene he's part of is funny in some way, shape, or form.
- Taught by Experience: When he realizes that two toughs are planning to kill him rather than just beat him up, he correctly predicts that Reese is about to break down the door and save the day. This is the third time his life has ended up in danger and he is able to spot the pattern.
- Too Clever by Half: The brains part is debatable, though. Sure, he's got the IQ and math skills, but the good judgement...
- Too Dumb to Live: Who would be dumb enough to have his number appear again 6 episodes later, and then again 11 episodes after that? He would.
- What Happened to the Mouse?: He disappears after season 2, leaving one to wonder where he went. Given his general propensity for getting into trouble, it doesn't speak highly of his chances.
The son of Paul and Joss Carter.
- I Have Your Son: Elias kidnaps him to get Carter to hand over the Mafia Dons. Reese promises to rescue him and she refuses.
- Parental Abandonment: His father suffered from a nasty case of untreated PTSD and, while he very much wanted to be involved in Taylor's life, he was only well enough when Taylor was a teenager. Taylor doesn't seem particularly bitter about it and he ends up living with Paul after Carter dies.
- Satellite Character: Only important because of his relation to Carter, and drops out of the story shortly after her death.
- You Are Not Alone: Constantly reminds his mother of this.
Joss Carter's ex husband, a former U.S. Army soldier who saw combat, and suffered from post-traumatic stress disorder as a result. Initially, he refused to seek treatment for his PTSD.
Lionel Fusco's son.
A skilled Con Artist who crosses paths with Team Machine, after which she finds herself working for a certain "Ernest Thornhill" - that is to say, the Machine's human alias.
- Becoming the Mask/No Name Given: "Harper Rose" is an alias, one of many. We've never been told her real name. She allows Team Machine to keep using the name after she ditches the identity because she "likes the sound of it".
- Boxed Crook: Becomes this after her introduction. She's still a con artist, but now the Machine/"Thornhill" is pointing her in the direction of dangerous criminals it wants out of the way.
- Companion Cube: It's hinted that the art deco ring she wears in "Blunt" is this.
- The Bus Came Back: After disappearing in the season 4 finale, she turns up in DC, working for an alternative Team Machine.
- Dark and Troubled Past: Hinted at.
- Deadpan Snarker: Even for a World of Snark like this series, pretty much every other line out of her mouth is some flavor of biting sarcasm. She can match Reese or Fusco in Snark-to-Snark Combat any day of the week.
- Femme Fatale: In her introduction, she seduced a worker at the marijuana store she was planning to rob and pretended to be his girlfriend for a few months. It seems that her feelings for him weren't totally insincere, though, since she helps Reese and Fusco save the guy's life after Dominic kidnaps him.
- The Fixer: One of her lines of business is making and selling forged IDs. It's how she ends up back on Team Machine's radar in "Skip", helping the criminal the Number of the week is chasing flee the country - though it's implied the Machine planned this.
- I Have Many Names: Also known in some places as "Athena" or "Fiona". Her actual name is never provided to the characters or the audience.
- Karma Houdini
- Loveable Rogue: The most openly criminal of Team Machine's allies, always looking out for her own benefit first and willing to scam most anyone for a quick buck. Reese still develops a grudging respect for her, because the majority of her targets are criminals much worse than herself, and when the chips are down her heart is (usually) in the right place.
- Nerves of Steel: Next to her manipulation skills, this is Harper's most defining asset.
- In "Blunt", she strolls right into the cartel's bar to elicit their help, knowing full well everyone there wants her dead. She doesn't even flinch when one of them pulls a gun on her at point-blank range. Then she leads the gangsters into the Brotherhood's hideout and stands unarmed in the middle of the Mexican Standoff that results long enough for the cops to arrive and Reese to save her boyfriend.
- In "Skip", caught in a gunfight between Team Machine and a team of hired mercenaries, she walks right into the line of fire and negotiates a cease-fire that ensures both parties get what they want without anyone getting killed.
- Only in It for the Money
- Pay Evil unto Evil: Her usual mode of operation. "I steal from criminals 'cause they don't call the cops." It's implied this is the reason the Machine hires her on as an asset after her introduction.
- Sherlock Scan: Very good at reading people. In her introduction alone, she pegs Reese as an ex-soldier after only meeting him twice, and masterfully manipulates both Dominic and the Mexican cartels by playing on their egos and vices.
- The Trickster: And how. She defines life by the ability to be free and enjoy yourself, and constantly plays everyone around her like fiddles (including Team Machine, though they've grown wise to some of her tricks by her later appearances).
- Wandering the Earth: Per her own words, "I don't plant roots so I can bail at a moment's notice".
- Wild Card: Ultimately, she's on no side but her own, though she is willing to work with Team Machine if it benefits her (at least partially thanks to the Machine manipulating things behind the scenes).