You know the drill. This is a listing of characters for The 39 Clues. Beware of unmarked spoilers!
Daniel Arthur "Dan" CahillOne of the series' two protagonists, and Amy's younger brother. The two of them were raised by their great-aunt Beatrice after the death of their parents in a fire, and are drawn into the international clue hunt at their beloved grandmother Grace's funeral. Dan is childish and excitable, but loyal and determined.
- Action Survivor: He and his sister begin the first series as unprepared young civilians thrown into a dangerous globetrotting chase, though by the Sequel Series, they have both Taken A Level In Badass, bigtime.
- Annoying Younger Sibling: At the beginning, he and his older sister are perpetually squabbling. In the end, he still gets on Amy's nerves fairly frequently, but they have been through a great deal together and have realized that their strengths and weaknesses balance each other out.
- Beware the Nice Ones: Dan's pretty good-hearted, at least compared to his clue-hunting rivals, but once he's decided it's worth hurting someone, he's not going to hesitate to do so.
- Beware the Silly Ones: Sure, Dan's a jokester, and that's exactly why you should watch out. He's great at tricking people.
- Break the Cutie: The events of the first series are what do this, but the effects aren't completely visible until the second series. But once they are, Dan begins to have some very dark thoughts.
- Brother-Sister Team: He and his sister Amy form Team Seven of the clue hunt and act as a team going forward.
- Character Development: As Amy thinks to herself in Into the Gauntlet. Dan goes from an irresponsible prankster to a levelheaded and rational young man.
- Chaste Hero: Justified, as he's only 11-13 in the series. (Also, he's probably seen from his sister's love life that romance only complicates things, and his life is complicated enough as it is—what with escaping homicidal enemies, trying to save the world, being an awesome ninja, and all that.)
- Cheerful Child: At first. He still acts lighthearted and goofy some of the time later on, but by that time, he's been through some serious Break the Cutie, and it seems that his humor is more of an attempt to cover up his darker thoughts and feelings.
- Class Clown: Apparently, he was one prior to the Hunt.
- Collector of the Strange: While Dan collects some normal things, such as baseball cards, he's also been known to collect odder things, like tombstone rubbings.
- Embarrassing First Name: Dislikes being called "Daniel."
- Family Eye Resemblance: Although he and Amy apparently don't look very much alike, they both have the same green eyes.
- Foolish Sibling, Responsible Sibling: The foolish to Amy.
- Guys Are Slobs: He's been shown on several occasions to be very sloppy, especially when food is involved.
- Heartwarming Orphan: The first book kicks off with both his parents already dead and him heading to the funeral of the grandmother who was the closest thing he had to a caring parental figure. Despite this, he spends much of the first series as a cheerful jokester who provides levity, in contrast to his more serious older sister.
- Hero with Bad Publicity: Wanted by Interpol as of Cahills vs. Vespers. However, he and Amy are only doing what they have to, cooperating with the Vespers to ensure the safety of the hostages.
- Hypocritical Heartwarming: Will get angry whenever anyone else insults/hurts his sister. It doesn't change the face that he also regularly makes fun of her, but it's sweet nonetheless.
- Justified Criminal: Sure, he and Amy often break into places where they aren't supposed to be and steal international treasures, such a priceless painting, but it's often portrayed as justified, because if they don't do it first, one of their rivals with (assumedly) less pure intentions will.
- Kid Hero: Eleven in the first series, thirteen in the second series, and lovably immature in both.
- Kindhearted Cat Lover: Like his sister, he's one of the nicest and most sympathetic characters (at least initially) and crazy about Grace's cat, Saladin.
- Little Miss Con Artist: A male example, when the situation calls for it. He may seem like an innocent kid, but don't be surprised to discover later that he's picked your pocket.
- Naïve Newcomer: To the world of the Cahills, at the start of the original series. By the Sequel Series, he's in just as deep as everyone else.
- Naughty Is Good: He is a mischievous Mouthy Kid who enjoys pestering his older sister, but he's definitely one of the good guys.
- Parental Abandonment: His parents were killed in a house fire.
- Photographic Memory: As Amy notes, it isn't completely effortless. He holds his breath to make sure he'll remember.
- Pursuing Parental Perils: He and Amy are searching for the 39 Clues, a quest that resulted in their parents being killed in a fire by their clue-hunting rivals.
- Rags to Riches: Everyone who passed through the gauntlet gained two million dollars, twice the amount offered in Grace's will.
- Screw the Rules, I'm Doing What's Right!: He and his sister will circumvent the rules if it's for the greater good. It's the reason for their roles as Justified Criminals.
- Sibling Yin-Yang: With Amy. Dan is hyperactive and excitable whereas Amy is shy and withdrawn.
- Sweet Tooth: Like many boys his age, Dan has a notable fondness for sweets and junk food.
- Tomato in the Mirror: When he and Amy learn that they are Madrigals, whom they had previously feared.
- Upbringing Makes the Hero: His and Amy's naivete in regards to the clue-hunting world is what gives them an edge against their competitors.
Amy CahillDan's older sister and the series' other protagonist. Bookish and intelligent, but less than confident at first, Amy comes into her own during the clue hunt and the events following it.
- Academic Athlete: Becomes one after the clue hunt ends and she decides to start training for the next crisis.
- Action Girl: Eventually becomes one, as exhibited nicely at the start of The Medusa Plot when she kicks a gun out of a man's hand after her and Dan's school bus was attacked.
- Action Survivor: Both she and Dan, until the start of Series Two.
- Bookworm: Called a "librarian in training," she's reading book when first introduced.
- Badass Bookworm: She starts off very easy on the "badass," heavy on the "bookworm," but then undergoes a lot of Character Development.
- Belligerent Sexual Tension: Has this with Ian and, later, with Jake.
- Betty and Veronica: The Archie in the center of the Love Triangle. At the start of the Sequel Series, she's dating Evan, but then, she develops a lot of BST with Jake. At the end of Cahills vs. Vespers, Evan is Killed Off for Real, and for now, Amy is with Jake.
- Beware the Quiet Ones: Don't let her shyness fool you: she's perfectly capable of defending herself and her family, as several of her enemies find out the hard way.
- Break the Cutie: Goodness, yes. See also: going into Heroic Safe Mode in Trust No One. Not to mention the death of her boyfriend Evan in Day of Doom.
- Brother-Sister Team: With Dan.
- Dude Magnet: Let's see, so far she's attracted the notice of Ian Kabra, Kurt, Evan Tolliver, and Jake Rosenbloom.
- Cute Bookworm: As stated above, she loves to read, and is extremely shy and prone to the blushing associated with this trope.
- Dating Catwoman: Has a brief romance with Ian in The Sword Thief. This ends rather badly.
- Family Eye Resemblance: She shares her green eyes with her brother Dan.
- Fiery Redhead: After she shakes off most of her Shrinking Violet behavior, she gains quite an attitude befitting her red-brown hair.
- Foolish Sibling, Responsible Sibling: Responsible, in contrast to Dan.
- Girl Next Door: Has the personality of one, being down-to-earth and kind, but is the main character (or, one of them) herself.
- Heartwarming Orphan: Like her brother, her parents were lost in a fire before the series begun. Combined with her Shrinking Violet personality (at least in the first series) and general niceness, makes her quite a sympathetic character.
- Hero with Bad Publicity: In the second and third series.
- Heroic Safe Mode: In the latter portion of Trust No One.
- Justified Criminal: Sure, he and Amy often break into places where they aren't supposed to be and steal international treasures, such a priceless painting, but it's often portrayed as justified, because if they don't do it first, one of their rivals with (assumedly) less pure intentions will.
- Kindhearted Cat Lover: Like her brother, she's one of the nicest and most sympathetic characters (at least initially) and crazy about Grace's cat, Saladin.
- Little Girls Kick Shins: In The Black Circle, she kicks Ian in the shin—very hard.
- Love Dodecahedron: Is at the center of one, with four Love Interests in Canon.
- Meaningful Name: "Amy" means "beloved." See also: Heartwarming Orphan; Dude Magnet.
- Memento MacGuffin: Grace's necklace that Amy always wears.
- Naïve Newcomer: At the beginning of the first series; by the Sequel Series, she's the de facto head of the Madrigals.
- Official Couple: At the start of Cahills vs. Vespers, she's dating Evan Tolliver, However, at the end of that series, he is killed in the fight against the Vespers, and she starts going out with Jake.
- Orphan's Plot Trinket: The jade necklace that she inherited from Grace.
- Pursuing Parental Perils: She and Dan are searching for the 39 Clues, a quest that resulted in their parents being killed in a fire by their clue-hunting rivals.
- Rags to Riches: At the end of the first series, she and Dan become millionaires.
- Red Oni, Blue Oni: The Blue to Dan's Red.
- Savvy Guy, Energetic Girl: Despite her calmness in contrast to, say, her brother, she is definitely the livelier in her relationship with the easygoing Evan. She also has this dynamic with Ian and Jake, two of her other Love Interests.
- Screw the Rules, I'm Doing What's Right!: She and Dan are forced to make the "abide by the law or do the right thing" decision a lot, and they inevitably do this.
- She Cleans Up Nicely: Judging by Ian's uncharacteristic reaction to her wearing a fancy dress in Rapid Fire: Fireworks.
- Shrinking Violet: In the beginning. By the last book, she's overcome a lot of it.
- Sibling Yin-Yang: With Dan. Amy is shy and withdrawn, whereas Dan is hyperactive and excitable.
- Significant Green-Eyed Redhead: Auburn-haired and green-eyed, as well as the closest thing the series has to a protagonist.
- Single Woman Seeks Good Man: Her boyfriend as of Cahills vs. Vespers is Nice Guy Evan.
- Smooch of Victory: Kisses Jake on the cheek (in front of her boyfriend Evan, no less) in The Dead of Night when Jake makes an important deduction.
- Speech Impediment: Her stutter, though it lessens as the series goes on.
- The Leader: Of the Madrigals and, by extent, the Cahill family. She's a leader of the Levelheaded variety.
- The Smart Girl: Has almost an almost supernatural talent for doing research, and good at thinking on her feet.
- Tomato in the Mirror: Learns that she and Dan are Madrigals.
- Took a Level in Badass: Between the beginning of the Clue Hunt and the start of Cahills vs. Vespers. Mousy Shrinking Violet —> Badass Bookworm Action Girl.
- Twin Telepathy: Though not twins, she and Dan can communicate merely via facial expressions, without having to utter a word.
- Unrequited Love Switcheroo: Ian fell for her just as she was beginning to (allegedly) get over her crush on him—although Crushed later showed that she wasn't quite as "over him" as she believed herself to be.
- Upbringing Makes the Hero: Her and Dan's lack of knowledge about the clues gives them a unique perspective on the Hunt, as well as keeps them from doing such reprehensible things as the other teams do to get clues.
- Uptight Loves Wild: Seems to be Jake's perspective, in which the rule-breaking Amy is the "wild" one.
- Young and in Charge: Becomes the head of the Madrigal branch and, to an extent, the Cahill family.
Nellie GomezThe Cahill children's au pair, who possesses a myriad of skills far beyond what a normal caretaker should have. She becomes protective of them and accompanies them on the clue hunt.
- Chekhov's Skill: Has many talents that come in handy during the clue hunt.
- Contrived Coincidence: Nellie's learned so many things that help the Cahills on their quest. Although near the end of the series it's revealed that Grace knew she'd end up being their nanny one day, so she paid for plenty of Nellie's learning (such as being trilingual and knowing how to fly a plane).
- Cool Big Sis: To Amy and Dan. She becomes an actual "big sis" to them, or at least family, when she becomes one of their legal guardians at the end of the first series.
- Dreadful Musician: Apparently, Nellie's musical talent... leaves quite a bit to be desired.
- Headphones Equal Isolation: Invoked; when Amy and Dan don't want her to listen to their conversations, they have her put her earbuds in.
- Kindhearted Cat Lover: Not only is she one of the most consistently nice characters in the entire series, she love Team Pet Saladin.
- Less Embarrassing Term: She says she signed on as an au pair and not a nanny, despite the fact that the former is basically just Gratuitous French for the latter.
- Mama Bear: Though her relationship with Amy and Dan becomes more reminiscent of a sibling bond, this still applies.
- Team Chef: Loves to cook and so is in charge of many of the meals.
The Cahills' pet Egyptian Mau. Originally belonged to Grace Cahill.
- Action Pet: It is implied that he helped Grace on her missions.
- Cool Cat: See above. No wonder he stays so collected with Amy and Dan dragging him around the world on all their adventures!
- Nonhuman Sidekick: To Amy and Dan in the first series. As of Cahills vs. Vespers, he is safe in the Comm. Center, pestering Ian.
- Team Pet: Goes everywhere with Amy and Dan. If he's there, they probably are, too.
- Trademark Favorite Food: He loves red snapper—so much that, in One False Note, he refuses to eat anything else. (However, in The Medusa Plot, it's shown that he has also developed a taste for caviar.)
Ian is introduced as Natalie's handsome, scheming older brother, befitting his status as a high-ranking Lucian. Like his sister, he joins the clue hunt on orders from his mother, whom he follows blindly.
- All Girls Want Bad Boys: Amy's early-series crush on him.
- Ambiguously Brown: He's described as having dark skin, but the only other clue to what ethnicity he may be is his last name.
- Animals Hate Him: Poor Ian. Buffy hates him, Saladin hates him...
- Becoming the Mask: His "I Was Only Pretending To Like You" toward Amy naturally stopped being such an act.
- Belligerent Sexual Tension: He and Amy have this during the Clue Hunt (and even a bit afterward).
- Betty and Veronica: The Veronica to Amy's Archie in terms of personality, but the Betty in that he seems to have known Amy for longer than Evan or Jake have. (He's said so himself: they have a "considerable history.")
- Break the Haughty: After his mother's betrayal, although he didn't take it as badly as Natalie. And then, it gets worse. In Cahills vs. Vespers, his sister is held captive by Vespers, and when they finally reunite, she is killed by the Vespers' Doomsday machine—actually bringing Ian to tears. Soon afterward, his mother dies, as well.
- Broken Ace: Let's see: devastatingly handsome, charming, very rich,manipulative, badass, can speak multiple languages and play the piano... but along with his many talents comes a lot of pressure and parental issues.
- Brother-Sister Team: Forms a team and acts in conjunction with his little sister Natalie, serving as something of Foils for Amy and Dan.
- Chick Magnet: He is said to have numerous girls fawning over him, though the only named character who has been shown to harbor an interest in him was Amy.
- Distracted by the Sexy: In Rapid Fire: Fireworks, the great Ian Kabra is rendered stunned by the sight of Amy in a fancy gown.
- Emancipated Child: He and Natalie emancipate themselves from Isabel in Into the Gauntlet.
- I Was Only Pretending To Like You: Pulls this on Amy...until it's revealed that he really does have a crush on her.
- Insecure Love Interest: The reason why he decided not to confess his feelings for Amy in Crushed was due to the fact that, after letting his mother go, he felt that he didn't deserve Amy.
- Mistreatment-Induced Betrayal: He and Natalie left their mother after the events of Into the Gauntlet.
- My Beloved Smother: Isabel is very controlling, but not in the least loving. Ian might apply as a Momma's Boy.
- Nominal Hero: In the Sequel Series. He is only cooperating with the Cahill siblings because the Vespers kidnapped his sister—or so he claims.
- Not So Stoic: He shows a lot more emotion than usual in Day of Doom—especially after his sister's death.
- Princely Young Man: The King/Spoiled Brat type initially, though it fades later on.
- Privileged Rival: How better to quickly establish the Kabras as the Cahills' rivals by, during the first time the audience sees the two teams speak to each other, establishing that they have a private jet and make fun of Amy and Dan for not having money?
- Riches to Rags: At least, in his opinion; although he and Natalie are still wealthy after abandoning Isabel, they aren't nearly as rich as before.
- Screw the Rules, I Have Money!: He thinks that "laws are for poor people."
- Siblings in Crime: With Natalie. And then, their mother gets involved....
- Smart People Play Chess: In One False Note, readers are told that Ian is very intelligent, and this is demonstrated by his decision to play chess against a super-computer.
- Smug Snake: Or, one might say, a cocky Cobra. He gets a little better after his HeelFace Turn, although he definitely still has his moments of arrogance.
- Spoiled Brat: His parents raised him to think that being a Kabra makes virtually everything your birthright.
- Stalker with a Crush: Operation Trinity shows him watching Amy come home from school via a surveillance camera (although, technically, the crush didn't really manifest until later).
- The Beautiful Elite: He and his sister are immediately established as rich, well-dressed, well-traveled, charming, and - of course - unbelievably good-looking.
- The Proud Elite: He's dark, described as very good-looking, and is extremely full of himself. He starts off pretty evil, but turns out to have hidden morals.
- The Rival: He and Natalie are a Brother-Sister Team like Amy and Dan, but with more money and resources. Ian is Amy's age, and Natalie is Dan's.
- Token Evil Teammate: In the Sequel Series, Cahills vs. Vespers, at least initially.
- Too Clever by Half: Is highly intelligent (he can beat a supercomputer at chess) but, as his sister notes, is somewhat lacking in common sense, which can lead him to make mistakes.
- Tyke-Bomb: Raised from birth to become a skilled Lucian clue-hunter.
- Unrequited Love Switcheroo: Fell for Amy just as she was beginning to get over him.
- Uptown Girl: A Gender Swapped example in his romance with Amy. Ian was raised in luxury, while Amy and Dan had a far more middle-class upbringing.
- Villainous Crush: His feelings for the heroic Amy Cahill.
- "Well Done, Son!" Guy: He's kind of a sucker for his mother's good opinion. As well as his father's, it would seem from The Black Circle.
- Wicked Cultured: His parents own an art dealership, and he has the appropriate education, and of course he can Mozart beautifully when presented with a piano, in contrast to the heroic Amy, who stumbles because her Aunt Beatrice stopped paying for her lessons.
Ian's younger sister who is just as scheming as he is. A Rich Bitch, she dislikes doing dirty work and aspires to please her mother in every way.
- Action Fashionista: She's quite handy with dart gun, and dreams of someday shopping in every country.
- Afraid of Blood: Hates the stuff, and strongly resists going near Nellie when the latter is wounded.
- Ambiguously Brown: She's described as having dark skin, but the only other clue to what ethnicity she may be is her last name.
- Annoying Younger Sibling: To Ian, occasionally. However, they are shown to care deeply for each other, just like Amy and Dan do.
- Break the Haughty: Her mother drinking the Lucian serum, then trying to kill her and Ian.
- Brother-Sister Team: With Ian.
- Depending on the Writer: While most characters suffer from this, it's especially apparent with Natalie. In the seventh book, she gets sick at the mention of violence. The next books describes her "merciless, piercing eyes."
- Emancipated Child: She and Ian declare themselves this in Into the Gauntlet.
- The Fashionista: Natalie is always whining about something spoiling her designer clothes.
- Girly Bruiser: A villainous version. At least, initially.
- Mistreatment-Induced Betrayal: She and her brother had their HeelFace Turn after their mother's treatment became too awful to bear.
- Privileged Rival: Like her brother, she quickly makes her rival status known by teasing Amy and Dan for not having as much money as she and her brother.
- Riches to Rags: After their HeelFace Turn and disowning their mother.
- Screw the Rules, I Have Money!: Throughout the series, Ian and Natalie get away with a lot because of their vast fortune.
- Siblings in Crime: With Ian.
- Spoiled Brat:m Her parents taught her that being a Kabra makes virtually everything your birthright.
- The Beautiful Elite: She and her brother are immediately established as rich, well-dressed, well-traveled, charming, and - of course - unbelievably good-looking.
- The Rival: She and Ian are a Brother-Sister Team like Amy and Dan, but with more money and resources. Ian is Amy's age, and Natalie is Dan's.
- Tyke-Bomb: Like Ian, she was trained by her mother to become a clue-hunter and dangerous Lucian agent.
A South Korean businessman hailing from Seoul, Alistair made his fortune from selling the microwavable burrito. But by the time of the series his money is running out and he swaps the million dollars for a hint to the first clue. He is an Ekaterina. Throughout the series often offers to help Amy and Dan, but they are openly distrustful of him, as he seems fond of double-crossing them.
- Friendly Enemy: He may be a rival to Amy and Dan in the clue hunt, but he's always perfectly polite and nice to them, even when he's stabbing them in the back.
- HeelFace Revolving Door: Amy and Dan can never tell whether to trust him. His record of both helping them and leaving them behind is constantly growing.
- Inscrutable Oriental: Alistair is always polite, even at the worst of times.
- Intergenerational Friendship: With Amy and Dan—well, sort of. Becomes purely a friend later on, once he joins the Madrigals.
- Inventor of the Mundane: His money comes from his invention of his pride and joy, the microwavable burrito.
- Never Found the Body: The Sword Thief: While escaping a cave in Korea. Amy and Dan seem genuinely grieved by his death - until they find his glove and realize that he must have left them.
- Obi-Wan Moment: Spends his final moments either telling the others to be brave or that they are brave.
A Lucian ex-KGB agent who agrees to trade the one million dollars for a hint to the first clue at Grace's funeral. Throughout the series, Irina works behind the scenes, following Amy and Dan and threatening people with her poisons. By the time the sixth book rolls around, however, it's revealed that there's way more to her than we originally thought.
- Action Girl: A grown-up version. She was a KGB agent, after all.
- Dark Action Girl: As a former KGB agent in an American series, naturally she's a pretty shady - and dangerous - character.
- A Death in the Limelight: In Too Deep gives her character a lot of development. She dies at the end of the book.
- HeelFace Turn: Genuinely wants to help Amy and Dan by In Too Deep. That doesn't end up too well for her.
- Heroic Sacrifice: Sacrifices her life saving Amy, Dan, and Alistair from a fire set by Isabel.
- Mistreatment-Induced Betrayal: What caused her to betray Isabel.
- Redemption Equals Death: After several books of gaining sympathetic backstory and showing an increasing willingness to help the heroes, her redemption arc culminates in her sacrificing her life to rescue Amy and Dan from a fire in In Too Deep.
- Rogue Agent: So she claims. In actuality, she works for Isabel.
- Russian Guy Suffers Most: She lost her son, was treated as a servant by Isabel, and finally dies in a fire when Isabel sees it a bother to rescue her.
- Sacrificial Lion: You know the newly-introduced Isabel is a real threat when Irina dies in the fire she set. That wasn't Isabel's goal (she was after Amy, Dan, and Alistair instead, but it's the first fatality of the hunt and after several books without a casualty, the death drives home how dangerous the competition is.
Jonah WizardInternational hip-hop sensation and teen idol, Jonah fits very nicely into the family's Janus branch. His mother is the famous Cora Wizard, who set up his career. Jonah joins the clue hunt to please her. At the beginning he is only concerned about his public image, but after he befriends Dan in The Emperor's Code this begins to change.
- Big Brother Mentor: Plays this role to Dan in The Emperor's Code.
- Chekhov's Skill: Who knew his love of Shakespeare would seriously come in handy in the gauntlet?
- Chick Magnet: Naturally, seeing as he's a world-famous musician.
- Damn, It Feels Good to Be a Gangster!: Even though he lives in a nice, comfortable home in Beverly Hills.
- Friendly Enemy: Later on in the Clue Hunt, he becomes genuinely amicable towards the protagonists.
- Heterosexual Life-Partners: He and Hamilton become close friends are usually mentioned together in Cahills vs. Vespers.
- Idol Singer: He's a world-famous hip-hop star, with the Fan Girls, merchandise, and ego to go with it.
- Momma's Boy: He's close to and always tries to please his mother Cora. Until he defies Cora and the two become estranged.
- Paparazzi: Is constantly plagued by them, which makes his job as a Janus agent difficult.
- Teen Idol: An Idol Singer in his teens, with many a fangirl.
- These Hands Have Killed: His reaction after shooting Luna Amato at point-blank range in Shatterproof.
- "Well Done, Son!" Guy: He wants his mother's approval.
The HoltsA Tomas family consisting of Eisenhower Holt, his wife Mary-Todd, and their children Hamilton, Madison, and Reagan, the Holts excel at everything athletic but are not the brightest crayons in the box. Out of the five of them, Hamilton is the most sympathetic, and is the one who forms alliances with Amy and Dan.
- Academic Athlete: Hamilton is later revealed to be this instead of Dumb Muscle, as he's mentioned to have done well on the SATs.
- Action Girl: Reagan and Madison can pack quite a punch.
- Alliterative Name: Hamilton Holt.
- Badass Family: The entire family excels in everything physical.
- Big Brother Instinct: Hamilton seems to show a bit toward Dan and Amy later on in the first series. Once, he protectively refers to Dan as "my little buddy."
- Dumb Blonde: The Holts are blonde and, usually, not very bright.
- Dumb Muscle: Their hat. As Tomas, they're very good physically but can't quite keep up intellectually with everyone else.
- Flanderization: Hamilton started off as a Genius Ditz who could barely read, but had a talent with computers. By The Medusa Plot, though, he's portrayed as actually a pretty smart guy who did really well on the SAT.
- Geek: Hamilton knows a lot about computers.
- Genki Girl: Day of Doom compares Reagan to the Energizer Bunny, as she is constantly keeping the other hostages active and helping them keep their strength up.
- Genius Bruiser: Hamilton has a talent with computers and did well on his SATs.
- Heterosexual Life-Partners: Jonah and Hamilton become close friends are usually mentioned together in Cahills vs. Vespers.
- Lovable Jock: Hamilton grows into this; despite being as jock-ish as the rest of his family, he becomes a genuine friend to Amy and Dan later on.
- Sickeningly Sweethearts: Mary-Todd and Eisenhower, surprisingly. For such aggressive people, they sure are openly affectionate with each other.
- Theme Naming: The entire family is named for American historical figures — Eisenhower and the twins for three former presidents, his wife Mary-Todd for Mary-Todd Lincoln, and Hamilton for Alexander Hamilton.
- Theme Twin Naming: Madison and Reagan.
- Took a Level in Kindness: Whereas family gatherings once meant the whole family harassing Dan and Amy, they become much less violent after the clue hunt and Hamilton becomes a friend.
The StarlingsGenius thirteen-year-old triplets who turn down their three million dollars in favor of the Clue Hunt. All three are Ekaterina, but are taken out of the first clue hunt fairly quickly. Out of the three it's Sinead who we get to see the most of.
- Alliterative Name: Sinead Starling, the most prominent of the three.
- Big Bad Friend: Is the Vesper Mole, to her best friend Amy's dismay.
- Brainy Brunettes: Have auburn hair.
- Break the Haughty: All three start as Insufferable Geniuses, but this happens to Sinead after the explosion. This may have prompted her face heel turn.
- The Bus Came Back: Sinead and her brothers are out of the hospital by Into the Gauntlet.
- Evil Redhead: Sinead, although she later realizes her error and makes a HeelFace Turn.
- FaceHeel Turn: Sinead is revealed to be Vesper Three, the Mole. Not that she was incredibly kind in Maze of Bones as a Cahill, but still.
- Fangirl: In an online mission, Sinead is revealed to be a big fan of Taylor Swift.
- HeelFace Revolving Door: Sinead starts out as an enemy, then turns good at the end of Into the Gauntlet, then becomes The Mole for the Vespers, then joins the Cahills again.
- Put on a Bus: They're taken out of the hunt by an explosion at the beginning and sit out most of the story as a result. (Well, it was really more like an ambulance).
- Sacrificial Lamb: Although they're not killed, the Starlings are severely injured early on in the clue hunt to show the readers that the competition is Very Dangerous.
- Sibling Team: Together, the three triplets make up Team Three of the clue hunt.
- Significant Green-Eyed Redhead: Sinead. Her significance is that she's a Teen Genius, as well as Amy's best friend. And—oh, yeah—the Vesper Mole.
- Teen Geniuses: All three of them.
- The Mole: Sinead.
- Theme Triplet Naming: Ned, Ted, and Sinead.
- Took a Level in Kindness: Although, in Sinead's case, it was at least partially phony.
- Well-Intentioned Extremist: Sinead is working with the Vespers in hopes of being able to cure her brothers. When she realizes that the Vespers will not be able to help her, she makes a HeelFace Turn and rejoins the Cahills.
Grace CahillBeatrice's younger sister, Hope's mother, and Amy and Dan's grandmother, she was one of the last genuinely nice Cahills. Amy and Dan were her favorites, and they spent almost every weekend with her. After her death, her will offers either one million dollars or a hint to the first clue to select relatives.
- Chekhov's Classroom / Someday This Will Come in Handy: The little tidbits of information she gives Amy and Dan help in the clue hunt.
- Death by Origin Story: Her death kicks off the series.
- Kindhearted Cat Lover: One of the few family members who are kind to Amy and Dan before the clue hunt, and very fond of her pet, Saladin.
Arthur Trent and Hope CahillAmy and Dan's parents. They died in a fire and were avid clue hunters. Arthur was the one who got Eisenhower expelled from West Point Military Academy.
- Adventurer Archaeologist: Hope was one by profession.
- Death by Origin Story: They were killed in a fire prior to the events of the first series.
- Deceased Parents Are the Best: Played with a bit. Though Amy and Dan initially remember their parents nothing but fondly, once they learn that they were Madrigals, their feelings are briefly called into check. In the Sequel Series, something similar happens when the siblings find out that Arthur was a Vesper.
- Defecting for Love: When Arthur met Hope Cahill, he was a Vesper. He stopped his Cahill-hating ways once he married her.
The Man In BlackInitially, a mysterious character who seems to be following the Cahill siblings as they hunt for clues.
- Badass Grandpa: Despite being a great-uncle, he shows some serious combat skill in Day of Doom.
- Long-Lost Relative: The Cahills' great-uncle.
- Right Hand vs. Left Hand: Amy and Dan initially see him as an enemy, but realize that they're playing on the same team.
- Shrinking Violet: He's nearly as shy as Amy is before she undergoes major Character Development.
- The Men in Black: Is referred to as one throughout the series all the way until Book 9.
- Walking Spoiler: His actual purpose and identity are kept secret until the ninth book.
Isabel KabraIan and Natalie's mother, a Lucian whose elegant and superficial exterior conceals a great deal of wickedness.
- Abusive Parents: And how. To her, the safety and mental health of her children are a small price to pay to accumulate power.
- Big Bad: Of the first series. In the Sequel Series, she is the Dragon to Vesper One but ends up taking him down in a blaze of glory.
- Bitch in Sheep's Clothing: Her ticket out of prison is starting an organization dedicated to global disaster relief.
- Dying Moment of Awesome: Kills innumerable Vesper mooks effortlessly and manages to take out Vesper One himself after consuming the master serum, dying as she destroys the Doomsday machine that killed her daughter Natalie.
- Evil Matriarch: Until the very end of Day of Doom, when she becomes a Mama Bear, consumes the serum, and goes on a Roaring Rampage of Revenge after Natalie's death.
- Eyes of Gold: Has amber eyes like her children.
- Kill 'Em All: Her plan in the gauntlet.
- Mistreatment-Induced Betrayal: The reason why Irina and her own children abandoned her.
- Pinocchio Nose: Ian notes the corner of her lip tightening when she lies.
- The Dragon: To Vesper One, seeing as she is Vesper Two.
- The Fashionista: She can have you murdered and look good doing it.
- "Well Done, Son!" Guy: Both of her children seek to gain her approval (especially Natalie).
- With Great Power Comes Great Insanity: After she drinks the Lucian part of the master serum (giving her ultimate intelligence and strategic skills) it's hinted she finally snaps.
- You Killed My Father: Amy and Dan towards Isabel (along with others) once the truth of their parents' death comes to light. But she takes the chief blame for acting like a cocky idiot and burning the house down recklessly, along with threatening their child.
Bae OhAlistair's uncle, who raised him after the death of his father. He is the leader of the Ekaterina branch.
- Evil Uncle: He's completely willing to murder family members if it gets him somewhere. Then again, that's not so unusual for Cahills... but Bae's willing to kill immediate family members, which seems to be much more taboo among them.
Cora WizardJonah's mother.
Broderick T. WizardJonah's father.
- Character Tics: His BlackBerry is perpetually in his hands.
- Conflicting Loyalty: Eventually, between his wife and their son. He chooses Jonah.
William McIntyreGrace Cahill's lawyer and a friend to Amy, Dan, and Fiske. He is Killed Off for Real in the Cahills vs. Vespers series.
- Cool Uncle: Amy and Dan call him "uncle," even though he was actually their father's cousin. (He and Arthur grew up thinking of each other like brothers.)
Nataliya Ruslanova Radova
- Double Agent: For the Madrigals.
- Chuck Cunningham Syndrome: The Viper's Nest seemed to be setting him up as a possible Love Interest for Amy; however, he's never heard from again.
- One-Shot Character: Only appears in one book.
LesterA helpful young man that the Cahills encounter in Storm Warning.
- Cruel and Unusual Death: Death by drowning in quicksand—after he got caught in it when he was trying to help Isabel's henchmen get out of it.
Beatrice CahillGrace's older sister, an eccentric old woman who could care less about the Cahill family history.
- Crazy Cat Lady: She has a thing for ceramic cats.
- Elderly Blue-Haired Lady: Mentioned as having blue hair in Maze of Bones.
- Inferiority Superiority Complex: Her harsh attitude towards everything Cahill is later explained in "The Black Book of Buried Secrets" to be because [she couldn't handle the pressure put on by her sister and brother, who excelled in all the tests.
- Jerkass: Is beyond nasty to her great-niece and nephew.
- Maiden Aunt: She would fit the trope if Amy and Dan were remotely fond of her. Instead, she is merely a...
- Resentful Guardian: She clearly resents being saddled with her sister's grandchildren. Amy and Dan feel the same about her and don't mind being taken care of primarily by a series of au pairs.
- You Should Have Died Instead: Actually feels this way towards Fiske, because their mother died giving birth to him.
Vikram KabraThe father of Ian and Natalie and the husband of Isabel. Thus far, he has not appeared in the series in the flesh.
Evan TolliverIntroduced in Vespers Rising as a boy who goes to school with Amy and Dan. In The Medusa Plot, he has been dating Amy for several months. After the Cahills fend off an attack by the Vespers in full view of Evan, he becomes understandably confused, and gets even more confused and upset when Amy cuts off contact with him in fear of him finding out about her family history. Eventually, however, Evan does find out about the Cahill story, as a result of his immediately being able to identify the obscure type of cell phone that Vesper One is using. Also because of this, Evan is invited to join Ian and Sinead at the Cahill Command Center, and helps them do research to aid Amy and Dan in their missions around the world.
- Death of the Hypotenuse: He dies in Day of Doom, leaving Ian and Jake as Amy's love interests.
- Dying Moment of Awesome: Although previously a Non-Action Guy, he helps the Cahills in the fight against the Vespers in Day of Doom and seems to be fairly good at it. It is during this fight that he is fatally wounded by a gunshot.
- Fire and Ice Love Triangle: The Fire, in contrast to Ian or Jake.
- Geek: He knows a lot about computers and technology.
- Kindhearted Cat Lover: Takes good care of Saladin while Amy and Dan are away from Attleboro.
- Nerds Are Sexy: Amy finds him completely Adorkable.
- Nice Guy: And seeing who he's up against, this gives him a distinct disadvantage.
- Non-Action Guy: In contrast to his girlfriend. However, he fights fairly well alongside the Cahills in Day of Doom... although he dies in the process.
- Second Love: To Amy, after Ian.
- Single Woman Seeks Good Man: Amy does, and that good man is Evan— although her affections slowly switch targets to Jake.
- Smart People Wear Glasses: In case his talent with technology didn't establish him enough as a nerd and appropriate love interest for Amy, he also wears glasses.
- Stalker with a Crush: Shows shades of this in The Medusa Plot after Amy cuts off contact with him due to problems with the Vespers, going so far as to sneak onto the grounds of Grace's mansion to find out what's going on. This behavior stops once Ian explains the Cahill-Vesper conflict to him.
- Taking the Bullet: Tries to do this for Amy when Vespers stop the schoolbus and confront the Cahill siblings in the beginning of The Medusa Plot. Rather oddly subverted, as by this time Amy has gone through Character Development and proceeds to kick the gun out of the man's hand and hold off the attackers with her martial arts skills. In Day of Doom, he does end up taking a bullet, although not for any other character in particular.
- Understanding Boyfriend: Not only is he far more understanding than many people would be, but he is also very helpful to the cause.
Casper WyomingA character, not the place. A Vesper who was named after a city where his parents robbed a bank. He's proud of that.
- Brother-Sister Team: With Cheyenne, although he harbors a bit of resentment toward her for replacing him as Vesper Six.
- Siblings in Crime: He and Cheyenne—and seeing as their parents named them after bank robberies they committed, it apparently runs in the family.
- Theme Twin Naming: Both he and Cheyenne are named after their parents' bank robberies in (alliterating) cities in Wyoming.
Cheyenne WyomingLike her twin, Casper, Cheyenne is a character not to be confused with the city. She is pretty dangerous, especially when she's working alongside her brother.
- Brother-Sister Team: With Casper, though she has shown a willingness to sabotage him if it suits her purposes.
Atticus RosenbloomA genius eleven-year-old friend of Dan's.
- Catchphrase: "In actuality..."
- Child Prodigy: And how. Eleven years old, and he's completed high school in his "spare time."
Jake RosenbloomThe older brother of Atticus.
- Betty and Veronica: The Veronica in the Evan/Amy/Jake Love Triangle. (No say on which role he would take when contrasted with Ian.)
- Big Brother Instinct: His display of this for his little brother is what causes Amy to decide he isn't so bad, after all.
- Fire and Ice Love Triangle: The Ice, as opposed to Evan's Fire.
- Official Couple: With Amy, as of Day of Doom.
- Smooch of Victory: Amy Cahill gives him a jubilant kiss on the cheek in The Dead of Night when he makes a big discovery, leading a stunned Jake to utter the infamous "Wore yelcome."
- Third-Option Love Interest: For Amy Cahill. She chooses him in Day of Doom, though it remains to be seen whether this relationship will last in the third series or not.
- Uptight Loves Wild: The "uptight" in contrast to Amy's "wild." However, once he realizes why the Cahills do the things they do, he loosens up a bit.
Milos VanekAn Interpol agent tracking Amy and Dan across the globe.
- Badass Normal: Well, he's not a Cahill, Vesper, or Guardian, as far as we know, but he still manages to be a fairly epic guy.
- Chuck Cunningham Syndrome: He was chasing Amy and Dan for most of the second series, and even temporarily got them a couple of times. He was featured prominently in Shatterproof and then was never mentioned again.
- Reasonable Authority Figure: Not at first, but he begins to show shades of this in Shatterproof.
Luna AmatoAn Interpol agent who trails Dan and Amy through Europe.
- Affably Evil: Initially treats Amy and Dan kindly, but is later revealed to be a Vesper.
Gideon and Olivia CahillThe parents of Luke, Katherine, Thomas, and Jane Cahill. Gideon invented the master serum which is made by combining the 39 ingredients revealed by following the eponymous Clues.
Luke CahillThe oldest Cahill sibling, and the founder of the Lucian branch.
- Badass Cape: Wears one later in life, when he works as a royal advisor. It adds to his menacing appearance.
Katherine CahillThe second-oldest Cahill sibling, who founded the Ekaterina branch.
Thomas CahillThe third-oldest Cahill child and the founder of the Tomas branch.
Jane CahillThe fourth-oldest Cahill and the founder of the Janus branch.
Madeleine CahillThe last child of Gideon and Olivia Cahill, born after Gideon's death, who founded the Madrigal branch.
J. Rutherford Pierce
- Corrupt Corporate Executive: Head of a media empire, a position he abuses to destroy the reputations of Amy and Dan and garner support for a presidential run (as a stepping stone to world dominance.)
- Take Over the World: His goal is to use the presidency to turn the United States into a dictatorship and then start a world war in order to rule the world.
- Villain with Good Publicity: He's a media mogul, so of course the media loves him, at least if they want to keep their jobs.
- Woman Scorned: Male example. He never forgave Hope Cahill for turning him down, and since someone already beat him to the punch in killing her, he decides to take it out on her children. With slander - and murder.