!!Don Eppes (Rob Morrow) [[quoteright:203:http://static.tvtropes.org/pmwiki/pub/images/don_eppes2_708.jpg]]

* BerserkButton: Threatening or hurting Charlie is a surefire way to piss off Don.
* BigBrotherInstinct
* BrainsAndBrawn: The brawn to Charlie's brains.
* ChickMagnet: Seriously, the guy has had at least five girlfriends.
* FairCop
* InformedJudaism: Starts out lapsed but becomes more interested in Judaism over the course of the series.
* KnightTemplarBigBrother: When one guy went after Charlie, Don walked right into his office and told him right to his face that he would take him down hard for going after his brother.
* SiblingTeam: With Charlie.
* SiblingYinYang
* TheStoic
* TeamDad
* TheUnfavourite: Not intentionally, but due to being a math child prodigy, Charlie required a lot more of their parents' attention when they grew up. Alan has some guilt about it and Don initially has some resentment, but they get over it.

!!Charlie Eppes (David Krumholtz) [[quoteright:233:http://static.tvtropes.org/pmwiki/pub/images/xxx_6665.jpg]]

* AbsentMindedProfessor
* {{Adorkable}}
* AnnoyingYoungerSibling: He is younger than Don by 5 years. While he didn't pester him, Charlie's advanced mind often made things awkward for the both of them growing up.
* BadassBookworm
* BrainsAndBrawn: The brains to Don's brawn.
* BrainyBrunette
* DefectiveDetective: Charlie, a mathematical genius who uses his talents to help his FBI agent brother solve crimes, has emotional difficulties to the point that he locks himself in the garage to work on unsolvable problems when he can't deal with life. However, he overcomes this early on.
* GentlemanAndAScholar
* GoodWithNumbers
* HollywoodNerd
* InsufferableGenius: He can be this at times, especially when confronted by a rival.
* InterdisciplinarySleuth
* JewishAndNerdy
* NiceJewishBoy
* NonActionGuy
* TheProfessor
* QuirkyCurls
* ShorterMeansSmarter
* TheSmartGuy
* SmartPeoplePlayChess: To the point that the only chance they have at beating him is for two people to play him while also distracting him.
* TheStoryteller: Charlie teaches math with stories.
* TheStrategist: Charlie would probably qualify with his ability to mathematically predict the moves of evildoers.

!!Larry Fleinhardt (Peter [=MacNicol=]) [[quoteright:209:http://static.tvtropes.org/pmwiki/pub/images/larry_fleinhardt_7489.jpg]]
* AbsentMindedProfessor
* BunnyEarsLawyer: A very bright and valuable man; he even went into space once. However, he also sold his home out of not wanting to constrain himself and once had a diet of only white foods, among other quirks, such as staying in bathtubs for a long time.
* CloudCuckoolander
* TheGamblingAddict: A former one, and his experience comes in handy when a prior colleague of his does the same scheme they did when they were younger -- card-counting.
* GentlemanAndAScholar
* TheLancer: To Charlie.
* ParentalIssues: Not to the extent of Megan, but he had problems with his father wanting him to become an artist.
* TheProfessor
* SesquipedalianLoquaciousness
* SmartPeoplePlayChess
* TheSpock

!!Alan Eppes (Judd Hirsch)

* GoodParents
* InformedJudaism: Is lapsed and didn't make it a major influence in his sons' lives.
* IWantGrandkids: Alan takes the proactive approach, giving solid relationship advice to Don and Charlie.
* TeamDad
-->'''Alan:''' I'm going to give you the same advice I give to all the geniuses I know.
-->'''Larry:''' And that is?
-->'''Alan:''' Don't be an idiot.
-->'''Larry:''' Ah. (nodding)

!!Amita Ramanujan (Navi Rawat)[[quoteright:216:http://static.tvtropes.org/pmwiki/pub/images/amita_ramanujan_5536.jpg]]

* ArrangedMarriage: Amita was in one and knew the guy as a good friend since she was young. [[spoiler: Her parents invited him back to try and win Amita over, though them and Charlie were unaware that he was ''gay'', making the situation awkward but funny.]]
* BollywoodNerd
* BrainyBrunette
* TheChick
* GamerChick: As revealed in the episode "Primacy". Even when she was supposed to lose, her gaming reflexes kicked in and she won anyway.
* HotScientist
* HotTeacher
* [[GentlemanAndAScholar Lady and a Scholar]]
* LadyOfWar: In "Primacy" and other episodes.
* ParentalAbandonment: Not quite, but Amita's parents are always too busy to visit her.

!!David Sinclair (Alimi Ballard) [[quoteright:250:http://static.tvtropes.org/pmwiki/pub/images/numb3rs_david_9308.png]]

* BaldBlackLeaderGuy: Although not technically a leader, he is Don's second-in-command.
* BlackBestFriend
* HeterosexualLifePartners: With Colby.
* TheLancer: To Don.

!!Colby Granger (Dylan Bruno)

* TheBigGuy
* ColdSniper: Of course, all the FBI agents have to be this to a degree, but somehow Colby ends up having to shoot criminals more often than the others.
* DeadpanSnarker
* [[spoiler: FakeDefector: Colby turns out to have been a triple agent for several years. This causes a fair bit of drama and angst, since the rest of the cast find out about the "defector" part well before they find out about the "fake". ]]
* HeterosexualLifePartners: With David.
* HiddenDepths: Is fluent in Spanish, which comes in handy when the team investigates the case of missing Spanish girls.

!!Megan Reeves (Diane Farr)[[quoteright:228:http://static.tvtropes.org/pmwiki/pub/images/megan002_7436.jpg]]

* ActionGirl
* DeadpanSnarker
* FormerTeenRebel
* LadyOfWar
* NerdsAreSexy: Dates Larry, to everyone's surprise.
* ParentalIssues: Has a serious problem with her dad that resurfaces every now and again.
* TheProfiler
* WhyCouldntYouBeDifferent: According to her, she was her father's "last attempt to get a son."

!!Liz Warner (Aya Sumika)

* ActionGirl
* LadyOfWar

!!Nikki Betancourt (Sophina Brown)

* ActionGirl
* DeadpanSnarker: Often manages to outsnark Colby.

!!Terry Lake (Sabrina Lloyd)

* TheProfiler

!!Ian Edgerton (Lou Diamond Phillips)

* AntiHero: Out of the FBI, Ian's the one most willing to use extreme means to complete his task, most apparent during "Ultimatum", and shows no hesitation in killing. He's still an overall a good guy, though.
* {{Badass}}: You bet it! It sort of comes with being the fifth?.. [[YouDoNotWantToKnow Fourth?..]] [[BrickJoke Third]] best sniper in the country. He lives up to the reputation, too. If he's in an episode, he'll usually outshine the agents by being the one to take out the criminal of the week.
* ColdSniper

!!Robin Brooks (Michelle Nolden)

* HelloAttorney
* HeroesWantRedheads: Don's on-again-off-again girlfriend. [[spoiler: And fiancee, by the end of the series.]]