When a character is primarily a nerd (or possibly Geek), but still manages to pull off feats of Action Heroism, then they are a Nerd Action Hero.
Sometimes this is the result of Character Development, where the character starts out as a nerd but over time develops heroic skills. In other cases, the character is a Hidden Badass.
Sometimes a Nerd Action Hero may be paired with an Action Girl in a Strong Girl, Smart Guy duo, and the aforementioned Character Development may occur as a result of their interaction.
There is an overlap with Badass Bookworm, but many of those are badass first and bookworm only as a bonus. There can also be an overlap with Science Hero, but a Nerd Action Hero tends to do more ordinary Action Hero things (shooting, fighting, jumping, etc.) when the action starts.
Compare the Super Loser, an uncool superpowered being, and Super Zeroes, who are ineffective at heroism. For characters who generally take Guile Hero or The Smart Guy roles to the point where viewers might even forget they're devastatingly effective at getting physical, they might have Minored In Ass Kicking. Can also be a Working-Class Hero if the nerdy hero is also from the lower working-class backgrounds. Compare Pop-Cultured Badass, who is often this trope.
- Throughout the Haruhi Suzumiya series, due to all the strange things that happen to Kyon, he develops into this. However, after a while, he leaves things to Yuki. After the Disappearance (Vanishment) movie, though, Kyon has the ability to bargain with aliens that have godlike powers.
- Izuku Midoriya from My Hero Academia is a hero Otaku to the nth degree, to the point that he memorizes the favorite foods and trees of the world's most famous heroes. After obtaining One For All, he eventually becomes a brawler who rushes into the middle of the fight to deal serious hurt and overpower his opponents with his Super Strength, going so far as to break a limb if he needs to use 100% of his new power. But his greatest strength is his nigh-encyclopedic hero knowledge and knack for strategy.
- Valierie from Danger Girl is a nerd first and an Action Girl second, so she qualifies. Abbey, on the other hand, is an Action Girl first and bookworm second. And third comes JC from the video game adaptation, who's more of a Wrench Wench who can kick ass as nicely as she can defuse bombs.
- In Amazing Fantasy, Izuku is surprised when Bakugou doesn't refer to him as a nerd once in the first ten minutes they're sitting next to each other at the U.A. Entrance Exam. It's immediately lampshaded how pathetic that sounds.
Izuku: Oh man, that just sounds sad...
- The main protagonist in The Librarian starts out as an overage student who doesn't know when it's time to stop accumulating degrees and get a job instead—quite nerdy. Then he gets a job which requires him to be the hero.
- Indiana Jones would probably appear as this to one of his students or neighbors, as college professor = nerd, but since we in the audience mostly get to see him in the field he probably doesn't qualify.
- His father from The Last Crusade, though, is a more traditional archaeologist and not suited for the antics that Indiana finds himself in. He still manages a few brilliant feats.
- Milo Thatch in Atlantis: The Lost Empire starts out as an out-and-out nerd, but mans up and leads the final assault on the bad guys.
- All the main characters from The Last Lovecraft: Relic of Cthulhu qualify, but top marks must go to Paul, who leads the bad guys away to save the two remaining heroes, gets knocked out, backflips out a window, and then runs across the desert with two broken arms, before asking for some dynamite be shoved down his pants so he doesn't feel left out.
- In Broken Arrow (1996) Terry attacks one of Deakins's henchmen who she assumes is just a computer nerd, but finds out the hard way that he's a former Navy SEAL. Not enough is revealed about him to put him firmly in either this or the Badass Bookworm camp.
- Marvel Cinematic Universe has Spider-Man, who uses battle strategies from The Empire Strikes Back and Aliens. He also compliments Falcon and Winter Soldier on their tech while fighting them.
- Neal Stephenson is fond of these:
- Cryptonomicon: Randy Waterhouse spends most of the book as a pretty ordinary computer programmer, even though the fact that much of his company's business is in the Philippines brings some travel. At the end however, he gets thrown in prison for a while, develops some badass, and comes out as a fully-capable action hero just in time for the Final Battle.
- Snow Crash: Hiro Protagonist is a programmer who in real life is pretty close to broke (after having failed his pizza delivery job) and lives in a self-storage facility, although he also own a pretty large chunk of prime real-estate in cyberspace (think IP address block) on account of having been one of the guys who created it. As it happens, he is also the greatest swordfighter in the world (though he mostly gets to demonstrate it in cyberspace) and turns out to be good at other acts of Action Heroism as well.
- Zodiac: Sangamon Taylor is an analytical chemist who spends most of his time (most of the words in the book, anyway) looking for traces of compounds with covalent chlorine (and other toxins), and talking to people about these issues. He also engages in a lot of spy-like activities (covert intelligence gathering, sabotage, misdirection, etc.) before the action gets really hot.
- Although in his own narration, Harry Dresden portrays himself as a hardboiled detective, narration from his friends in side stories reveals he's really more this trope. Karrin Murphy in particular makes note of how things like his height can be either "awkward" or "imposing" and his pop-culture knowledge can come off as clever quips or like a fact-checking nerd. She figures that being the kid who grew too tall before he got coordination is what made him such a stalwart defender of the weak: he's a Bully Hunter at heart.
- Sourcery has Nijel, a weedy kid who's taking a Correspondence Course in heroism (of the barbarian variety) and ends up being pretty good at it. Good enough to run off with Conina, daughter of the Disc's most famous hero.
- InCryptid: Antimony is an Action Girl, skilled in combat, and pretty socially adept (plus she has fire powers), and also a huge geek. Her first mission as leader was to a comic convention.
- The main premise of N.E.R.D.S. is that a bunch of nerds with braces, glasses and horrible fashion senses are secretly child superspies tasked with saving the world.
- Daniel Jackson of Stargate SG-1 eventually developed into this. He started out as the bookish archaeologist / linguist of the team, usually wielding only a sidearm and having to be defended by others while he translated the inscriptions on whatever ruins they investigated. He continued multiclassing into badass thorough the series, becoming as competent with weapons and military tactics as the soldiers on the team. This becomes extremely obvious in the season 8 two-parter finale Moebius in which we get a peek into an alternate timeline where he didn't gain said badass levels and remained a meek nerd.
- Rodney McKay of Stargate Atlantis, who started out ejecting the clip from his gun while attempting to fire it to carrying and effectively wielding a P-90 and acting just as physically competent as Sheppard, the Lt. Colonel team leader.
- Harry Sullivan of Doctor Who is mostly an awkwardly old-fashioned ex-public school medical doctor, although with a military past. He is, however, mostly useful in his stories when he and the Doctor sneak up on two aliens and punch them in the back of the neck, and other such feats. (He was originally supposed to be a Badass Bookworm to compliment a frail and elderly Doctor but Tom Baker was unexpectedly cast instead, and Cast Speciation forced Harry into focusing primarily on his old-fashioned doctor traits while still providing backup for the Doctor in action scenes.)
- Scott Wolter of America Unearthed fame is often described as a "real-life Indiana Jones", being a Forensic Geologist investigating archeological mysteries.
- Wesley's character development across Angel tracks his development from pure book nerd to wannabe badass to actual badass... who is still happiest when buried in books.
- This trope is all over the place in The Flash (2014), especially in Team Flash. Cisco is a Gadgeteer Genius who has some combat training (and picks up metahuman powers as well), both versions of Harrison Wells are pretty badass, and Patty Spivot is a dorky police detective who enjoys reading Barry's lab reports and leaves to become a CSI herself. Barry Allen himself evenly splits the difference between being a nerd and an Action Hero — he catches bad guys both as a CSI tech and as the Flash.
- Billy, the Blue Ranger of the Mighty Morphin' Power Rangers. A walking stereotype of a nerd, complete with a Technobabble way of speaking, Nerd Glasses, and overalls. Becoming a Ranger actually improves his nerd cred, since now he gets to tinker with the super-advanced technology of the Command Center and and thus is able to create a horde of impressive machines, as well help make minor upgrades to their Zords, that aid in their fight against the forces of evil. In subsequent seasons, he gets much less stereotypically nerdy, reducing his technobabble speech, and wearing less baggy clothesnote , as a result of Character Development and becoming a much more confident fighter.
- Gordon Freeman from the Half-Life series. He's a theoretical physicist who, in the course of an experiment, accidentally opens a portal through which aliens start pouring out, devastating the laboratory he's stuck in. He quickly becomes an Action Survivor, fighting his way through the aliens and the human military sent there as a cover-up operation.
- Judging by their quotes (such as Lightning Bolt! Lightning Bolt), Taser Specials from PAYDAY 2 are a mix between this, Nominal Hero, and Hero Antagonist.
- Gaige in Borderlands 2 is a Nerd Action Anti-Hero who is just as capable of running around Pandora with a huge Torgue rocket launcher or shotgun as Krieg (who's nearly a foot taller than her, with washboard abs that are permanently on display). Of her three skill trees, Ordered Chaos is the most Action Hero-y, with a focus on hurling inaccurate but devastatingly powerful bullets at people, and science is mostly applied for the purpose of making the traditional violence more effective (such as using digistruct technology to create claws with which to rip people's faces off).
- The two playable characters from Wolfenstein: Youngblood fit in this category. Despite being trained early on to fight if needed, they really just start out as nerds without actual combat experience, owing their combat prowesses entirely to a pair of powersuits. Their rooms are what you'd expect: posters, personal computers, toys, books, all with the 80's atmosphere the game is known for. Their banter and attitude, if a little questionnable, also reflects the tone as well.
- In Grrl Power, there is Sydney, the comic-book store owner with a nerd's physique and outlook on life, who becomes one of Maxima's team of superheroines.
- John from Homestuck is quite the geek through and through (mostly about terrible movies, but also generally) and is generally something of The Fool, but as the comic evolves, he manages some pretty damn badass stuff.
- Then there's his ectobiological father, Jake English, who thinks he's a Hollywood Action Hero but is let down by such traits as his massive enthusiasm for every movie that has ever been made and his bizarre fusion of Antiquated Linguistics and random profanity.
- Space Dread from Val and Isaac is the most famous mercenary in the galaxy, a shapeshifting black mage, expert knife thrower, and the one responsible for most of the comic's unironic action sequences (and she's a mercenary in the "only targets serious criminals" school, so she does count as a hero). She also wears a Cosplay costume as her work attire, has a non-work wardrobe made up entirely of Lemon Demon Fun T-Shirts, does jobs to get graphics cards for her MMOs or DVDs of obscure cartoons, and became a mercenary by complete accident due to misunderstanding what sort of guild she was in; she originally wanted to be a juggler.
- The Angry Video Game Nerd may be a stereotypical geek, but when he has to deal with entities that threaten his life, he sure knows how to use a light gun.
- Jericho of the Whateley Universe is Black and Nerdy. He's an inventor at Whateley Academy. He's working on power armor designed to help firemen and emergency medical technicians in combat areas. But he's also on a training team with Eldritch, Diamondback and Razorback. This training team is widely felt to be the scariest team on campus.
- Dexter in Dexter's Laboratory has his moments in the show, being a super scientist with an assortment of cool robots and gadgets, but it really becomes true for his Future Badass version seen in Ego Trip.
- Rick from Rick and Morty is the smartest being in existence and is capable of all kinds of action whenever needed. Although he acts too cool to care most of the time, at heart he's a Manchild that mainly applies his super intellect to making awesome fictional things like Voltron mechs real.