24: This show is full of characters who have taken up multiple levels of Badass. These include Teri Bauer, Kim Bauer, Chloe O'Brien in season 4 (see also Crowning Moment of Awesome), George Mason (see also Heroic Sacrifice), Wayne Palmer, and Milo Pressman (total geek in season 1; to taking bullets in season 6). Some of the bad guys pull this off as well (Behrooz Araz and his trusty shovel in season 4 is the premier example)
Perhaps the biggest example is Tony Almeida who began season 1 as by the book systems analyst and by Season 7 reaches a level of badass that only Jack out badasses. This is never as evident as in season 4 when Tony is who Jack calls when he needs a rescue.
Charles Logan: from hand-wringing, indecisive coward to ringleader of massive conspiracy
Jack Bauer himself, who starts off as an (admittedly capable) secret agent-slash-family man who can eventually shrug off all forms of torture and come back from the dead. Also Nina Meyers, who starts off, again, a capable agent, who's a mole, but a pretty plausible one, and ends up becoming an unstoppable force of pure evil.
In Auction Kings, Jon goes from being "The new picker" in season one, to being "My [Paul's] picker" in later seasons.
Lennier is introduced as a mild-mannered, monk-like Minbari religious caste-member with a zen-like philosophy who is surprisingly shown a few episodes later to be able to defend himself with martial arts and take out a whole room full of drunk people, which is fair enough. However, by Season 4 he is fully capable of taking out multiple opponents belonging to the Minbari warrior caste trained almost from birth in the art of unarmed combat. This is before he joins the thousand-year-old organisation of elite badasses from beyond badassery in the final season who train up his badass skills to something on the other side of preposterousness.
Lyta Alexander starts off as a fairly mild-mannered woman. After telepathically scanning the injured Ambassador Kosh, she is Put on a Bus for two years before coming back as a much tougher, more skilled and more enigmatic character. Her increased telepathic (and beyond) powers are only revealed little by little, while at the same time she starts to show more vulnerability — until the fifth season, when the death of Byron causes her to stop playing it safe and show just how powerful she's become.
Vir Cotto starts off as an ineffectual, bumbling, yet thoroughly nice and sweet guy... yet slowly starts showing intelligence, confidence and deviousness to the point where he ends up succeeding Londo as Ambassador and later as Emperor, while throughout still remaining a thoroughly nice and sweet guy. When Vir takes a level in Badass by borrowing Londo's ceremonial sword and taking care of a Drazi spy, the result is so awesome they have to lampshade the lampshade.
Sheridan: What did Londo have to say about it? Zack: He was like a proud father. "Now he is a man..."
Battlestar Galactica (2003): Interestingly, the civilian characters of Ron Moore's show have been immune to this (with the exception of those revealed to be Cylons), although Laura Roslin becomes a political badass. Considering military officers like Adama and Cain, the badass market of Battlestar is cornered.
However, the TV movie Razor is all about Kendra Shaw being molded into a badass by Cain.
Also: Saul Tigh. In the first 2 seasons he's an alcoholic Commander Contrarian, but in the first 5 episodes of Season 3 alone he loses an eye, sends men on suicide missions against the Cylons, shuts up Laura Roslin, poisons his wife, and executes collaborators by airlocking them. He has remained awesome ever since.
In fact, he seems to take another level in badass after he finds out he's a cylon. One of his plans involves going and standing in an airlock threatening to space himself unless he gets what he wants (it makes more sense in context).
Being Human: Annie definitely takes a level after refusing to pass to the other side although one could argue that it began after she breaks her emotional bond to her boyfriend/killer.
The biggest part of her level up occurred when she went from being a ghost to being a poltergeist.
Angel's transformation as he moves from Buffy's season 3 into his own spinoff is particularly striking. From the very first episode, he's playing at the Badass Level Cap, drawing inspiration, according to director commentary, from the best moments of both Batman and John Wayne.
Wesley is a long-term, visibly executed case, marked with actual Character Development. It wasn't just the writers' decision to make him suddenly "cool" — it was the character's decision to. When first seen on Buffy, Wes was a weak, weaselly wimp. In Angel, he enters on a motorcycle, dresses in badass chic, and presents himself as a "rogue demon hunter", but at first remains his old self. As seasons go by, he becomes the series' Jack Bauer in every regard, only overshadowed by Angel himself.
Willow starts as a geek and bookworm, helpful only as research type. Her powers increase with time until by the end of Season 7, she is a super-powerful witch (and fully in control of her abilities).
Giles first appears to be a reversal, when in Season 2 it turns out he used to rank among the darker characters before joining the Watchers' Council. Shortly he proves to be ready to unexpectedly beat the crap out of his old friends and be one of the few that can stand up to season 6's Dark Willow. Another example from season 5, episode 19 "Tough Love":
Slook: No words shall pass my lips that would bring peril to Glorificus. Giles points his finger to the counter, without taking his eyes from the minion. Giles: Girls, get the twine that's on the counter. Let's tie him up. Willow and Tara turn away, the camera is following them. Suddenly we hear a small, nasty cracking noise. Slook cries out in pain. Slook: Don't! Oh! I'll tell you... anything. Please! ... Whatever you want! Just—arg!—anything! Anya: What happened? Giles:(matter-of-factly, almost ironic) He changed his mind.
Dawn is a relatively mild example, apparently in her spare time picking up reasonably fluent Turkish and Sumerian, and eventually in Conversations With Dead People proving capable in magic.
Spike's flashbacks follow his progress from a vampire who gets lucky when fighting a Slayer to one that specifically goes out after slayers, confidently tracking down and killing his second. After going through a reverse process in Buffy, his resurrection in Angel is every bit the badass, taking on the titular character Angel himself and winning.
Ultimately, it can be argued that any character who interacts with the main cast in the Buffy/Angelverse long enough ends up gaining levels in Badass, to the point where later seasons have a number of perfectly human characters taking down monstrosities that would previously be considered unkillable by anything short of a Slayer. The only choices for people around The Slayer and The Champion are: run far, far away; get horribly killed; or level up.
Xander goes from being rescued by Buffy in Season 1 to "Did you see that? I hit a guy!" to actually fighting off vampires for quite a long time in "School Hard", Season 2. He also changes from mocking how scared he is to standing up to Angelus. Angelus is The Joker in vampire form, in a scene where his balls drop a foot and triple in size Xander scares him off to protect a sick Buffy. Also in the season eight comics Xander has become a high tech battle watcher for Slayer Inc. He also wants people to call him Sgt. Fury.
Lilah Morgan spent the first 2 seasons of Angel as an ineffective Smug Snake. Then in season 3 she grew a spine and gained a lot of badly needed IQ points, turning her into a proper Magnificent Bastard.
Cordelia gained a very noticeable level in badass at the beginning of Season 2 of Angel, jumping into the fray during fights, and when she saves Gunn's friend's life in "First Impressions."
The Scoobies seem to accumulate levels of badass over the course of the show, particularly over the summers of 1998 (between season 2 and 3) and 2001 (between season 5 and 6), to compensate for the Slayer's absence.
The entire graduating class of 1999 gains a level in badass when they take off their graduation robes to reveal their arsenal of medieval weapons.
During the final battle of Season 8 of Buffy in the hole in the ground formerly known as Sunnydale, Andrew is seen killing several demons. He takes another level when he drugs Buffy and puts her mind into a Buffybot he built so she can be protected. Naturally, Buffy and Spike give him hell for it.
Harmony takes one in "Harm's Way," in which she stops a war between two demon races and finds and stakes the vampire who set her up for murder.
Lorne's last scene. Interestingly, it is obvious that Lorne finds the act disgusting and demoralising; afterwards, he walks out on the team without so much as a goodbye.
The Senior Partners. Granted, it took them potentially millions of years; Illyria was aware of the original Wolf, Ram and Hart in her own time - but they were as ultimate evil as vampires are in the present day. It's immediately pointed out to her that things have rather changed in the intervening aeons.
Between Seasons 2 and 5, Lindsey apparently learned a bunch of kung-fu and got a bunch of mystical tattoos making him invisible to the Senior Partners.
Burn Notice: Madeline Westen might need to be the new poster woman for this trope. We've lost count of the actual levels she's taken, but she starts out a nagging, hypochondriac chain smoker in the pilot and over three seasons, has become virtually equivalent to a spy herself.
Best demonstrated in "The Hunter", where Sam and Fiona are interrogating a pilot to find out where Michael has been taken. Sam gives up the questioning when the pilot makes it clear he's not afraid of anything, and goes to think through new options with Fiona. Madeline calmly walks out to the garage where he's being kept, lights a cigarette, and comes back 4 minutes later with the coordinates, having not even had to TOUCH the pilot.
There's an excellent moment in the season 3.5 opener, "A Dark Road", when she outright blackmails a woman she's become friends with because the woman possesses information that Michael needs to save lives. She hates it, but she stonewalls the woman and gets the files.
She shows off her Mama Bear status in the season three finale when she stalls and misdirects a set of government agents who only very slowly come to realize that she's not an innocent old woman. She tips Michael off that the FBI is at the house, then sends the feds on a wild goose chase. This whole time she is interrogated in her own home, given photographs of bad stuff Michael has supposedly done and she doesn't even flinch, but she pretends to crack to keep the agents fooled. When they finally threaten to arrest her for aiding and abetting, she practically puts the handcuffs on herself, and oh, yes - slaps a federal agent.
To show her new badassery, when Michael tells Sam and Fiona that she's trying to hold them off, Sam says "She's good, but she's not that good." When a former Navy SEAL thinks you're tough, that's saying something.
This isn't the first time said Navy SEAL acknowledges her badassery - from "The Hunter":
Madeline: Sam, let me remind you you're sleeping in my guestroom. You call me or God as my witness I will smother you in your sleep.
In the series finale, she takes one last level at the end by sacrificing herself to buy Jesse and grandson Charlie time to get away from James' mooks.
Canada's Worst Driver: The contestants are trying to take levels in competence. The host, however, can genuinely be said to have taken a level in badass driving after eight seasons of demonstrating driving challenges.
Charmed: Piper deserves a mention. Between her developing the ability to blow stuff up in Season Three, and her stepping up to the role of eldest sister, with accompanying increase in "don't mess with me" attitude, after Prue dies at the end of the Season Three, she certainly becomes more badass as the series progresses.
Chuck: The second season finale. "Guys, I know kung-fu," indeed.
Chuck takes additional levels throughout the series. After losing The Intersect he begins studying the spy craft on his own and claims to be gaining competency. This comes to a head in "Chuck Vs. The Santa Suit" where Chuck tricks Shaw into uninstalling his own Intersect, and then Chuck beats Shaw in a fair fight. Keep in mind that Shaw was still a fully trained, lethal CIA killer before The Intersect, and Chuck still beat that. Level up!
Chuck also shows this trope can apply to inanimate objects too - in Season 1, Sarah's "workplace" had nothing but a gun hidden in the mayonnaise. Then in Season 2, the stock room turns out to be a fully decked-out underground base.
The same applies to Buy More. After it burns to the ground, the NSA rebuilds it and turns it into a high-tech command center with the customers completely oblivious.
Chuck's friend, Morgan Grimes, also gets to take a level of bad-assery during the course of the show, with his Crazy Awesome stunts impressing John Casey, the Operation Bartowski team's resident badass. This comes to a head in Season 5. As Morgan becomes the Intersect. It didn't stick, however.
The Closer: Captain Sharon Raydor used to be an Obstructive Bureaucrat who made life hard for Brenda and her team; now she's helping them gun bad guys down in the streets. With a rifle. Perhaps unsurprisingly, Raydor went on to headline the spinoff series Major Crimes.
Community: Appears most notably in the paintball episodes where Greendale devolves into a chaotic paint-splattered warzone. Annie, who starts off as an often naive and innocent young woman, died rapidly and fruitlessly in the Season 1 paintball episode "Modern Warfare". By the time Season 2's western-themed "A Fistful of Paintballs" rolls around she's become a one-woman killing machine, dropping no less than ten opponents single-handedly; a higher kill total than the rest of the group combined.
Additionally, in the Season 3 episode "Remedial Chaos Theory", we discover that sweet, innocent Annie now owns and carries a revolver. She does, after all, live in a bad neighborhood. Awesomely enough, this may also explain why Annie became a crack shot with paintball guns; she's been practicing with real ones.
Criminal Minds: To a lesser extent, JJ. She is almost always portrayed as the perky blonde. Cops always assume that she's just the media liaison, and most of the time she's displayed as such. It changes slightly when she takes out three dogs with three shots in Season Two's Revelations. And then she becomes one of the coolest people, ever, when she gets a headshot on a criminal holding a hostage at gunpoint. If this doesn't sound particularly awesome, consider the fact that she shoots through the FBI seal on a solid glass door.
Not so lesser: in early seasons she's rarely seen with a weapon and rarely on the scene during the capture/arrest/takedown. Lately she's just as likely as Prentiss to be busting into a building packing heat. If her family ends up threatened by a killer has have almost all the other members, one suspects a full blown Mama Bear incident and local police cleaning up what's left of the threat in Aisle 5.
At the end of the most recent season she beat the tar out of a psychotic UnSub who had taken her son hostage. So I think the matter's been settled.
CSI: NY: In episode 2 of the seventh season, lab tech Adam Ross goes from shy geek to bad ass when the killer of the episode tries to run him over with his car. Adam starts off with a flying tackle and manages to get in his share of punches then, when the killer turns his gun on Mac and Flack riding to the rescue, takes the guy down with a fluorescent light bulb to the back of the neck.
It helps that he's taking the murder of the week rather personally, having been talking to the victim on a video chat site just before the killing and therefore witnessed it.
Doctor Who: Mickey Smith does this twice. Or maybe it took two stages. At first a cowering if sweet natured nerd, he moves up a level during the year he's falsely suspected of his girlfriend's murder. He becomes a lot braver, even willing to die to protect his girlfriend's mother, as well as developing some impressive hacking skills. He goes up another level offscreen after several years of fighting Cybermen in an alternate universe. Last time we saw him as a full badass complete with deeper voice and BFG.
Rose gains this by the end of series 4.
Captain Jack. OMG Captain Jack. He goes from charming coward, albeit one who is willing to fight when he has to, to immortal charming wisecracking badass.
And of course Rory Williams becomes awesome over the course of two thousand years protecting the Pandorica. Also his hand was briefly a gun. He even has a badass title: The Last Centurion. He's considered one of the most badass characters in the series, and there are even Chuck Norris Facts-like lists about him. When he started out, the idea was basically "the real Mickey is a badass so we need a new one." He was the AdorkableButt Monkey boyfriend of the 'real' companion.
Rory's other half Amy Pond goes from a flirtatious Fiery Redhead to a full on Action Girl in her two series as companion. She even saved Rory from the Silence with two machine guns, and kills Kovarian in cold blood!
We can't forget Rose's mum Jackie, who got to carry a BFG and shoot a Dalek to smithereens alongside Mickey.
They're not the only ones to do it. Martha did this either when she protected "John Smith" from the Family of Blood or when she Walked the Earth for an entire year.
Anyone who watches Doctor Who knows the Doctor has the tendency to turn his companions into badasses. It could be argued that it's part of the reason why he takes companions in the first place. Davros, one of the Doctor's oldest enemies, accuses him of this specifically, saying that while he may have created the monstrous Dalek killing machines, the Doctor has transformed innumerable innocent normal people into weapons himself.
Nightmare in Silver: The Cybermen have apparently been spending their time off the show level grinding in both asskicking and cunning. The first one we see deactivates a self destruct device for the entire planet, and they only get tougher from there.
Or going from the meek and gentlemanly Fifth Doctor to the maniacal and anti-heroic Sixth. The crowner has to be going from the sweet and ditzy Eighth Doctor to renouncing the very idea of being a "doctor" in the healing sense and becoming someone who could destroy both the Daleks and all of Gallefrey if it ended the Time War.
The Event: Sean has been gradually taking one throughout the first season. Leyla isn't quite there but she's catching up.
Farscape: John Crichton takes multiple levels of badass over four seasons: he starts out as a clueless nerd, and by series end is so badass he manages to intimidate two entire galactic empires into leaving him the frell alone by threatening to wipe out the universe. THE ENTIRE FREAKING UNIVERSE! And what makes it badass is he can pull it off.
There's also the interesting moment in the Peacekeeper Wars where he explains to a priestess that he and his friends aren't soldiers. To be fair, he really isn't, but with all the fighting they've all done over the course of the series, it's understandable one might make that mistake.
A big part of it is that he's gone so insane that he's come out the other side.
The follow-up comic reveals that Scorpius is far from being done with Crichton. The same comic also shows Rygel becoming a true warrior and leader instead of a lazy monarch expecting things to be done for him. It's this that finally convinces his subjects to back him instead of his corrupt cousin. The Hynerian Empire is powerful enough as it is. Now imagine it with the new-and-improved Dominar Rygel XVI at the helm, commanding his subject's loyalty not because of his ancestry but because of who he is.
Rygel's level up was foreshadowed by a spirit painting Zahan did of him early in the series. Such a painting depicts the spiritual self, rather than the physical, and this painting looks like Rygel the First, who commanded the Hynerean Empire because he was exerything Rygel XVI would eventually become because of his exile.
Rygel also leveled up when he fought off repeated assaults by Charrids. This showed the other side of Hynereans: While they will prefer to run, hide, or bargain their way out of trouble, if you back them into a corner and give them no option but to fight you, they'll take you off at the knees to get the rest of you down where they can get at it.
Zhaan also quite literally took a level in badass when she moved from being a Ninth-Level Pa'u to a Tenth Level Pa'u.
Zhaan: I am now a Pa'u of the Tenth Level, able to protect.
Firefly: Wash may be a great pilot, but until "War Stories" he's not much of a fighter. Then Niska tortures him.
"Bastard isn't gonna get days."
Also, Inara, starting in Serenity when she sets of the incense flash bomb to allow her and Mal to escape the Operative, and later in the last stand when she has the crossbow-thing. She fires with as much accuracy and deadly calm as Jayne and Zoe. Granted, we are told in "Shindig" that Inara can fence, but it wasn't until the movie that she proved her worth in battle.
River is a unique example. She had already been turned into a Super Soldier by the Academy before the show began, but their Mind Rape techniques made her so unstable that she wasn't able to do much at first. Quite a few of the earlier episodes revolve around the crew needing to rescue a helpless River, and it isn't until "War Stories" that we get a glimpse of what she can really do. "Objects in Space" then shows that she's gained enough presence of mind to develop a cunning plot, and by The Movie she's unstoppable.
Friends : Chandler is referenced as being mediocre in bed a couple times over the course of the early seasons, until the famous scene where Monica gives him a diagram-based crash-course in pleasuring the female body. His girlfriend literally runs across the hall to hug and emphatically thank Monica following their next lovemaking session. Ends up being a good call on Monica's part, as when her and Chandler later enter a relationship she repeatedly describes him as the best sex she's ever had.
In that case, this trope could also be applied to Ross. In "TOW the Videotape", Rachel makes note of how Ross was working out before they conceived, and in the finale, upon waking up from having sex again, Rachel comments appreciatively that he's "learned some new moves" (which Ross attributes to receiving a copy of "Sex For Dummies").
Daenerys Targaryen progresses from a timid maid being prostituted for an army to an emancipating conqueror.
Heavily mixed with Had To Be Sharp, all of the remaining Starks as a whole came back greater individually than a the beginning of the War of the Five Kings.
Arya is slowly leveling up as the series goes on, as she undergoes her Training from Hell in Braavos and acquires the skills of the Faceless Men, the deadliest assassins in the world. Unfortunately it comes at a terrible psychological cost.
Robb Stark manages to raise and lead an army despite being less than half the age of most of his lords.
Jon, due to his status as a bastard son raised in a castle, was a societal outsider. By the end of season 6, he becomes a charismatic leader the whole North and the Wildlings are ready to follow.
Now in general, by the end of Season 6: the Starks' Hundred Per Cent Adoration Rating finally pays off. They manage to gather many new allies, most notably Brienne, Davos, Littlefinger (for now), and the Wildlings while still having the support of their vassals. With their support, Sansa and Jon manage to defeat the Boltons for good and retake Winterfell, reclaiming the North and becoming one of the most united and powerful factions of the setting just behind Daenerys Targaryen's army.
Samwell Tarly progresses from cowering in the training yard to taking a meaningful part in the defense of Castle Black and encouraging those who are frozen by fear.
Matt seems to have taken at least half a level in Volume 4.
Micah apparently took one in Volume Three. In Volume Four, he's adopted the codename "Rebel" and is organizing a resistance effort against the government.
Peter does this, twice. First, by actually getting a grasp on his powers after his training with Claude. Later, when his DEPOWERING followed by his new NERFED ability, he becomes one of the most strategically intelligent characters of the show.
House concludes with Chase becoming the brilliant diagnostician who gets the epiphanies and solves the cases, and he replaces House.
House of Anubis: This happened to virtually everyone, due to the mysteries.
Alfie went from being bullied by his best friend and trying hard to win Amber's affections, but by season three he had taken on a huge role in Sibuna, from coming up with plans, rescuing his friends and eventually attacking Sinner!Fabian to try and save KT. He also became much more serious and determined to follow through with the mystery.
Fabian was the nice guy who was also an extreme doormat. He eventually started becoming much more assertive, virtually attacking anyone who wrongs him or Nina and proving himself much tougher than he seemed at first. He even won the school dodgeball tournament against the rival team, who had obliterated the rest of his team before.
Mr.Sweet is the dorky, lovable principal of the school, Eddie's father, and a member of Team Evil. His badass side showed in season 3 when he started making plans and tricking Sibuna very well. However, this also made him take a level in jerkass.
JAG: Mikey, Bud's little brother, grows enough of a backbone to stand up to his father by the beginning of season eight.
Jeeves and Wooster: Gussie Fink-Nottle seems to magically develop the ability to stand up for himself to a certain degree by his last episode. This may be a reference to the P. G. Wodehouse novels, where Bertie comments on his sudden ability to speak in public. Turns out he got some help from Jeeves.
In Kamen Rider Den-O, Ryoutarou starts off as a pushover and is dependent on his Imagin allies taking over his body during fights. Later on, he gets his own fighting form and comes over as much more serious and determined than he was at the start of the show.
In Kamen Rider Double, Shotaro, despite already being quite a tough character normally, takes several levels in badass after the Utopia Dopant attacks his friends. This results in him finally taking up his mentor's hat, storming the Utopia Dopant's lair, outwitting and disabling one of the most powerful Dopants in the show, rescuing Wakana, and carrying her out of the base as it explodes, all without transforming. He also crosses over into Empowered Badass Normal when he becomes Kamen Rider Joker.
Kamen Rider OOO: Shintaro Goto has already being shown a few times as a very tough character without having to transform, but then in episode 38 he finally transformed into Kamen Rider Birth and proceed to pull a Big Damn Heroes saving Eiji/OOO and epically curbstomping Kazari, Mezool and Gamel
In Kamen Rider Kabuto, both Sou Yaguruma and Shun Kageyama become this after gained Hopper Zecters. Also Kagami, after gaining Gatack Zecter.
Leverage: Being Genre Savvy enough to realize their situation after "The Nigerian Job," Nate and his new team know they all need a grounding in each other's area of expertise. By the second season, they're all adept at a first strike (defending against non-specialized opponents, maintaining a short-term cover identity, lifting wallets, planning the Short Con, and cracking lower-level codes). Later on, they're able to mix things up and even combine skills for new strategies. By the final season, they're all up at least one level across the board.
Lost: Sayid is a badass to begin with, but in the post-island flashforwards, he's graduated to international hitman. Sun is also seen in "There's No Place Like Home" to take a level (or two).
Morgana, likewise, was the King's ward who spent most of her time being sheltered in the castle. Even though she was in combat training and could handle herself in a fight, became infinitely more badass in season three when she came back with magical powers and a successful plan to take down her father Uther and make herself queen. Unfortunately, the process getting there cost her her mental health as well as her morals. She gets even more awesome in the seasons afterwards, when she becomes a High Priestess of the Old Religion and the second most powerful mage in the series, to the point where everyone is terrified of her, even Merlin.
Merlin himself goes from moving things with his mind and no magical training at all to earning the title of "most powerful sorcerer ever" throughout the series. Morgana is the only one who poses any threat to him, and he takes her down with one shot in the Grand Finale. Oh, and remember how he got stuck in the crystal cave and missed Camlann in the original legends? In this version, he not only shows up to Camlann, but he curbstomps the entire Saxon army by making it rain lightning on the enemy troops. Too late for Arthur, unfortunately.
Monty Python's Flying Circus: Subverted Trope in the "Marriage Guidance Counsellor" sketch, in which mild Arthur Pewtey finds his wife stolen from under his nose by the title character. A cowboy gives Pewtey a level-up in badass — "you gotta turn, and you gotta fight, and you gotta hold your head up high" — which lasts for as long as it takes the marriage guidance counsellor to tell Pewtey to go away. So much for pathos.
NCIS: Timothy "Probie" McGee began his NCIS career as a nervous, yes-man like team sidekick/chew toy whose primary contribution to the team was his tech savvy. While that is still his most prominent skill, he's developed his confidence and physical skills and has become a true team member — able to give as good as he gets as far as his partner DiNozzo is concerned, make impressive pitches to the head of the entire place without blinking, and being the most quietly unnerving man in interrogation.
Person of Interest: Lionel Fusco started as a Butt MonkeyDirty Cop who for the most part needed Reese to save him on several occasions, and was reluctant to help save the victims of the week. Then the first season finale came by. Fusco and Carter made like Big Damn Heroes, and then later on he protected a model from the Armenian mob (at one point going Guns Akimbo), identified and took out a team of hitmen in seconds, and defused an IED with only 3 seconds of advice, a Swiss army knife, and sheer determined balls.
In a much greater way than Fusco, the Machine, who in "Mors Praematura" revealed itself to be a top-level chessmaster, brilliantly foiling Vigilance from two angles, and playing everyone to its own purposes. And even manipulating Root into being captured and imprisoned by Team Machine.
Power Rangers RPM: Both played magnificently and deconstructed a bit. Ranger Yellow was initially a Rich Bitch who took a level in badass to survive the razing of the planet, but she runs into problems when her new Action Girl career is interrupted by pre-badass commitments.
Ziggy, Ranger Green, first gets his powers without any kind of training whatsoever. And it is made very clear in his first battle. However, as the season is progressing, he, while still the least skilled fighter of the team, is undeniably improving, as he is no doubt receiving training off screen.
In the original Mighty Morphin' Power Rangers, Adam is an example of this. While he was overshadowed by his other teammates and some unfortunate dialogue (power of kissing, anyone?) during his run as a Ranger (only second to Tommy Oliver in the entire series history), he returns twice having taken quite a few levels in badass after he stopped being a Ranger. First is in Power Rangers in Space where he saves Carlos, the guy who replaced him, by jumping out of nowhere and attacking the Monster of the Week UNMORPHED. Later in the same episode when surrounded by said monster and a ton of mooks, he risks being destroyed when he uses his original damaged Mighty Morphin' morpher to save the day. He then shows up again for the 15th anniversary episode to lead a team of veteran rangers. Not only is he a muscular martial artist who runs a dojo, but when the team is attacked by an ocean of mooks unmorphed, all the younger Rangers use their super powers to beat them. Adam, however, just proceeds to dispatch the most mooks by using nothing but his martial arts skills. Finally at the end of the special he takes on the Big Bad (Rita and Zedd's son no less) single-handedly. Levels in badass indeed.
What? No love for Billy? The guy started out not knowing how to fight and spent his early days flailing when he wasn't in his Ranger form. About a season later, he's a much more competent fighter along the lines of a Genius Bruiser. He kinda lost it after hanging back in the sidelines after Power Rangers Zeo, though.
When we first meet Bridge in Power Rangers S.P.D., he's a competent Ranger but probably one of the looniest people who's ever been given a morpher. Flash forward to the 15th Anniversary Special and who enters the fray dual-wielding Delta Blasters at the bad guys? Bridge, who's now the S.P.D. Red Ranger, a much stronger hero, and still the loveable goofball we all know.
Works for villains, too. Trakeena in Power Rangers Lost Galaxy started out as the spoiled and whiny daughter of Scorpius. But after some Training from Hell and the latter's death, she takes command of his forces and becomes an even more dangerous villain Scorpius ever was. It gets even worse, when she gets forcibly fused with The Starscream, causing her to also take a level in jerkass, and turn all her Mooks into suicide bombers.
Elsa of Power Rangers Dino Thunder was once hurt by a single unexpected strike from an unmorphed Kira, and another time she and Zeltrax had to retreat from a battle because again being hit once was enough to take her out of the fight. She had a decent Sword Beam move, but only used it once. Then Zeltrax is removed from the picture (appears to die, later returns crazy, and rebels against boss) leaving Elsa the only Dragon. She rises to the challenge by returning with a new, longer haircut, and being able to match even a Sixth Ranger on her own. And that once-used attack returns with a vengeance. Is she powered by the hair like Samson or something?
Primeval: While they had already been improving during the show's first three seasons, Connor Temple and Abby Maitland both took a major level in badass when they were stranded in the Cretaceous.
Danny appears to be trying this. He's developing talent as an escape artist, freeing himself from handcuffs twice (and eluding the militia for several hours the first time) and faking an asthma attack to lure a militia soldier who was taunting him into a near-fatal beating. He even manages to land a good punch on Neville during the impromptu boxing match. Neville, for his part, seems to be encouraging this in an offhand way either out of sentiment as a father or possibly to recruit Danny to the Monroe side.
Aaron took a level when he was forced by Drexler to duel with Nora—Aaron turned the gun on himself, shot himself in the chest (actually, where he kept his flask, which absorbed the shot)—and then shot Drexler when Drexler came to check the body. He's been leveling up in almost every episode since then, to the point where even Miles no longer intimidates him.
Charlie. She killed a militia lieutenant in episode 7 and didn't even blink, and this was after she agreed to kill other militia soldiers in cold blood. She can kill without needing her crossbow, and has become fairly proficient with actual firearms. It's almost like she's Miles's kid, not Ben's.
Rachel (to Miles): "How is it that you are better for Charlie than I am?"
The Rebellion collectively looks like it's about to, courtesy of aid and advisors from Georgia. Subverted Trope, because in episode 17, a drone strike reduced the army from 300 men to 30.
Brutus on Rome. He starts out as a bit of a wuss and a coward and tries but fails to stand up to his mother. Even the murder of Caesar is unwilling on his part and he pretty much just succumbed to peer pressure, despairing once the deed is done. He hits a low point in season two but then he pulls himself together, mans up and ends up commanding an army.
Sliders: Quinn Mallory apparently took a level of badass during the Channel Hop from Fox to Sci-Fi. This was mostly a result of Jerry O'Connell's increasing creative control over the show, and, like the rest of the show by this point, came off as contrived and meaningless.
Smallville: Lana Lang traded in Wangst for her own secret organization and a willingness to kill if necessary - though she never actually did. And that was before she gained superpowers so she could hold her own against alien/mutant threats.
And let's not forget that in preparation for the superpowers, she underwent training to withstand torture, by doing things like applying hot metal to her own arms.
Clark himself finally became a decent fighter in the sixth season when he dealt with a Phantom Zone thug in an illegal TNA-like match. Most other times when he dealt with an enemy of a comparable power level, he would get thrown around like a rag doll before he could find a way to bounce back. With this match, Clark was in a really bad mood and legitimately traded blows with the guy, winning through skill and strength rather than dumb luck. Ever since, he has done markedly better with these throw-downs. And that's not even mentioning the fact that Clark's powers gradually increased each year as he matured and absorbed more solar radiation into his Kryptonian cells. He goes from being about as strong as Golden Age Superman in Season 1 (the season where bullets—while not lethal to him—could still slow him down, and your average mutant could still go toe-to-toe with Clark and give him a hard time) to the level of strength Superman has in the Christopher Reeve movies by the end.
Then there's Season 9: Clark's view of humanity was shaken by the events of Season 8 and he abandoned his human side to fully embrace his Kryptonian Destiny as Earth's protector. Cue him literally taking levels in badass from Jor-El's voice in the Fortress, resulting in Clark stopping trains from crashing to taking out entire rooms of Checkmate goons before they can kill a tied up Chloe. Beforehand, if Clark came up against another Kryptonian, he'd get his ass handed to him. In Season Six, he had to Batman Gambit Zod to beat him. In Nine? He goes toe-to-toe with an armed Kryptonian ninja, and wins. He fights General Zod to a standstill when they both lose their powers. At this point onwards, whenever Clark loses his powers, he isn't Brought Down to Normal, he's Brought Down to Badass.
Perhaps just as importantly, the show's villains also take a level in badass as the show goes on. In Season One, almost all the villains were relatively low-powered mutants (created by the kryptonite meteor shower in the Pilot) whose only motivation was their mutual obsession with Lana, and who were only able to challenge Clark because he himself was still low-powered and final battles often took place near the chunk powering the Monster of the Week. Then in Season Two, the meteor mutants are still around, but Clark is gaining more power...and the show starts to have him come into conflict with Lex's father Lionel, theMagnificent Bastard - the quote concerned Erwin Rommel, but trope's named that 'cause it was Lionel's Fan Nickname. He takes over as the definitive Big Bad of Season Three. Season Four introduces magic (one of Superman's only canonical weaknesses besides kryptonite) being used by Clark's opponents, and a conspiracy plot that would be brought back in Season Seven. Season Five features the introduction of enemies from Krypton, including General Zod and Brainiac, and has Lex Luthor start to grow into his future role as a supervillain mastermind. Season Six features more supervillainy from Lex, and the introduction of a plethora of alien super-criminals from the Phantom Zone. Season Seven features more of these, as well as the reintroduction of the conspiracy plot from Season Four and the return of Brainiac. Finally, Seasons Eight, Nine, and Ten (during which the show could have quite reasonably been renamed "Metropolis") featured Clark going toe-to-toe almost entirely with canonical DC Comics supervillains, culminating with a season-long war against Darkseid, arguably the Big Bad of the entire DC Universe.
The glimpse of the future in Season 10's "Homecoming" has future!Lois noting that by that point in the future, Clark has a whole collection of failsafes and alien tech ready and available to use against the increasingly powerful foes he's faced off against.
It's easier to tell who didn't take a level in badass in that show. Chloe got turned not only into a hacker and Mission Control, but also into an Action Girl and Green Arrow's Battle Spouse. Martha became not only a senator, but also The Chessmaster. Even Jimmy "Henry James" Olsen got to play James Bond rather convincingly.
Martha Kent took a few levels, starting out as a farmer's wife, then getting appointed the U.S. Senate after her newly-elected husband died. Then she created a Secret Identity, beating Washington's best at their own game as the "Red Queen".
Arguably the show itself. It went from being what many people described as "Dawson's Creek with superpowers" in Season One, to the first ever full-fledged Live Action DC Universe ever seen onscreen, complete with live action versions of even the most obscure characters from DC Comics, characters that one may never have expected to make it to live action. Nowadays, whenever anyone descries a live action show about superheroes, it's Smallville they compare it to. Not Batman, not Lois and Clark, it's Smallville. Whatever its flaws, the show at least deserves credit for that.
Sons of Liberty: Both Joseph Warren and John Hancock start out considerably less action-oriented than their peers. By the final episode, Warren is leading a battle and Hancock shoots a soldier who is about to kill Sam and Revere.
Stargate SG-1: Daniel Jackson started as The Smart Guy, and was at most armed with a Beretta, tasked mainly with translations and exposition on Earth's various pantheons. A couple seasons later, and he's upgraded to whatever automatic weapon the rest of the team's using, and holding his own as much as the career military characters.
Someone (possibly Jackson himself) handwaved this by mentioning that Jackson had received some form of combat training since joining SG-1. Which is rather understandable, given the kinds of situations SG-1 found itself caught up in on a regular basis.
This is also a big level up from how he was in Stargate. Although even there, he went from the adorkable nerd to staff weapon-wielding badass by the end of the film.
In a less spectacular form, when Daniel and Chaka have failed at diplomatic relations with the local Unas on a planet rich with Naquadah, and the human dig team were surrounded by hundreds of Unas lead by Iron-Shirt, Daniel suggests that they get down on the ground to avoid conflict. When the military man in charge of the dig team starts to refuse at this, Daniel gives him a glance, shouting that they have to drop down, and 'that is all' that they had to do. Made even more Badass due to the military man in question had yet to listen to Daniel in the first place.
In Stargate Atlantis, Rodney followed in Daniel's footsteps. In a first season episode he's terrified of the idea that he might actually have to use a gun to defend himself. Not too long later, he's laying down covering fire with a P90 and using cover like a trained soldier. Probably justified in both cases, as it wasn't an immediate change, and it seems like a matter of necessity given the situations they find themselves in. Rodney himself may be a partial subversion, as he still freaks out while killing Wraith, even though he seems good at it. This is also possibly due to his internal Chance of Imminent Doom meter; when it redlines, he gets Awesome.
Which was nicely lampshaded in the second season episode "Inferno" where Rodney yells at Sheppard for putting pressure on him and Sheppard points out this fact to him.
More recently, Dr. Keller is seen fighting off a Wraith with a stick long enough for McKay to shoot it. He asks where she learned to fight, and she mentions she's been taking sparring lessons.
Teyla had a hand-waved level in flying the ship single-handedly badass. Apparently a short lesson with the weapons officer is enough to run the entire ship.
Since most ships in the gateverse seem to be partly flown by psychic powers — including the Goa'uld's motherships, that isn't particularly surprising.
Rush in Stargate Universe qualifies too, being even more of an Insufferable Genius than McKay (the insufferable part). When his lover is killed by a former Lucian Alliance member, he hunts down the trained soldier on an uninhabited world and kills him by causing a stampede of the local wildlife and finishing off with a close-range shot.
Star Trek: Deep Space Nine: To a certain extent, Jadzia Dax. She starts off as a reserved, quiet young woman, but (especially after her experience meeting an incarnation of her high-living former host Curzon) abruptly metamorphoses into a blood wine-chugging, bat'leth-swinging, Samoan-fire-dancing, blood-oath-honouring, Worf-marrying-and-rough-Klingon-sex-having badass. Interestingly, Dax's next host Ezri went through an abbreviated version of this after she was introduced at the beginning of the seventh season, starting as a bewildered Fish out of Water and going on to do such things as hunting a serial killer and confronting her gangster-involved family (particularly after Garak reads her beads in "Afterimage").
Star Trek: Enterprise: Hoshi Sato, the nervous alien language specialist, is given retroactive martial arts skills which she uses during Dr Phlox's kidnapping. While it's likely Hoshi would have become more assertive after her experiences during the Xindi conflict, it would have made more sense for her to have used the more simple takedowns taught to the crew by Major Hayes during this time. But less cool, I'm sure.
Like the Millennium Falcon, the USS Enterprise NX-01 is another spaceship that takes multiple levels in badass. But this was a logical progression, when the ship first left Earth, Starfleet had no clue of the kinds of dangers out there. As the ship encounters various threats, the crew upgrades the ship's ass-kicking abilities on the go, Trip and his team build phase cannonsnote like phasers, only without the 'r' due to TNG establishing that phasers won't be invented until the 23rd century from scratch, Reed creates the proto-type force field and comes up with the Red Alert system, and T'Pol routinely improves the ship's sensors. After the Xindi invasion, the ship is retrofitted into a war-ship, complete with the introduction of the famous photon torpedoes.
In the pilot episode, the ship is only armed with plasma cannons, which can't hit the broad side of a barn. They promptly forget about them and refit the ship to fire spatial torpedoes.
Enterprise demonstrates that Starfleet, and humanity itself will level up considerably. At the show's beginning, the Earth has all of one ship capable of real deep space travel and anything approximating real weapons. We know from the previous series (chronologically later adventures) what kind of force Starfleet will become, but in one episode, Daniels brings Captain Archer to the future to witness the battle of Procyon Five, wherein Starfleet is now going toe-to-toe with transdimensional beings who posess the ability to alter physical space. And according to Daniels, they win.
Teen Wolf: Several characters in season two - Scott can now beat the crap out of two betas at once without breaking a sweat; Derek goes from being a pretty badass Beta werewolf to being THE badass Alpha. Allison gets trained by her hunter family and transforms from helpless little girl to badass with a bow.
And in "The Last Voyage of the Jimmy Carter", John shows he's continued leveling up in badass when he confronts Jesse and tells her he figured out who and what Riley really was, casually takes her pistol from her, lays out why he is and will be the future leader of mankind, and tells her that her plan to make Cameron kill Riley never would have worked to break them apart. Thoroughly awesome.
Well, he knows she won't shoot humanity's only chance against the machines.
Cameron herself levels up in the second season, though more subtly. For most of the first season and the first half of the second, she at best can draw even with other Terminators; being smaller than other Terminators makes her lighter and less physically powerful. She makes up for it, however, by fighting smarter and apparently doing research into various martial arts and weapons, until she's able to regularly tackle other Terminators and take them apart single-handedly.
Up to a point where a clever mook who knows about her weakness to electricity takes her down with a pool of water and a well-placed electrical cable. He then gets ready to cut open her skull while she's disabled, knowing precisely where her chip is and knowing he's got two minutes before she reboots....only to discover to his dismay that she's upgraded, right before his neck is pulverized.
Torchwood: Any member. None of the primary characters (except for Jack, and if you count flashbacks, perhaps Ianto) started off as badasses. Owen was a doctor, Toshiko was a mild-mannered scientist, and Gwen was a police constable, whose job mostly consisted of making coffee, cordoning off crime scenes, and breaking up bar fights. As a PC, she wasn't even issued a gun. By series 3, Gwen is firing at government agents and, in series 4, takes out a helicopter with a rocket launcher.
True Blood: Jason Stackhouse is a weaselly Butt Monkey for the first season and a half. But then the Fellowship of the Sun turns on him and he fights back, then spends the rest of the season constantly topping himself in badassery.
In season 4, Jason is now a full-fledged cop and is shown to be a lot more competent than the sheriff. All because his sister disappeared for over a year.
A villainous example with Marnie, who was a self-described doormat, giving people psychic readings. After taking up necromancy, she summons the spirit of a pissed-off witch and later starts running the show. It doesn't end well for her.
The Vampire Diaries: Caroline takes one at the beginning of the second season. This is a pretty natural reaction to becoming a vampire, but she manages to become a really awesome vampire with remarkable speed.
Elena, slowly but surely. It starts in "Haunted" when she goes after Vicki with nothing but a wooden plank to protect her brother, continues in "Unpleasantville" when she manages to hold off a vampire with just a few pencils long enough for Damon and Stefan to kill him, and becomes even more noticeable in "Let The Right One In" when she saves Stefan by staking Frederick with a vervain dart and momentarily incapacitating him and by offering Stefan some of her blood.
Then along came season 3, in which this intensified noticeably. After Stefan leaves with Klaus, and later turns off his humanity. Elena asks Alaric to train her, and not only does she do it physically (boxing, lifting weights) but also is instructed in weapons like stakes and vervain-granades and how to use them swiftly. The best example of this is a scene in 3x06, where she stabs Stefan in the stomach with a hidden double-stake, just to show her that she could, that she was strong and not a weak damsel anymore.Crowning Moment of Awesome, indeed.
She hits full badass on season 4, after she becomes a vampire.
Bonnie, as of late Season 1 can bring on a really nasty migraine in 160 year-old vampires with just a squinty, mean look. Throw in telekinesis and the ability to set fire to water with just her mind and she has the edge on most of the supernatural beings on the show except Katherine thus far. May become an example of Linear Warriors, Quadratic Wizards as the show progresses.
It's probably easier to name the characters in The Walking Dead who don't undergo this trope than the ones that run headlong into it.
Carol is likely the most notable (and long-term) example of this. At the beginning of the series, she is a Shrinking Violet who can't stand up to her abusive husband Ed, hides behind Shane during the fish fry attack, and is generally seen doing the group's laundry with the other women. Once Ed (and later Sophia) dies, she begins coming out of her shell and begins to exhibit more character traits and a more proactive nature. At the beginning of Season 3, she (along with Beth, noted below) have become well-versed enough that she can fire a rifle without flinching, and defends herself at several points. By the time Season 5 rolls around, she single-handedly assaults Terminus by herself to rescue Rick and the rest of the group, then pulls a masterful gambit as soon as she reaches Alexandria by pretending to be the meek unassuming woman she was at the beginning of the series. It's at the point where she's become just as popular as Rick and Daryl, and is arguably the most popular female character on the show besides Michonne.
Carl starts out as a sort of Tagalong Kid/load, that gets shot and ends up indirectly killing Otis due to needing medical supplies to survive said gunshot. In season 3 after a time gap of about 7 months, however, he becomes a badass. His skills are able to rival adult members of his group, and he saves Tyreese's group from zombies by himself with little effort. Oh, and he killed his own mother (at age 13), to stop her from returning to life as a walker. Without crying. Near the end of Season 5, when Rick finds his son outside the walls of Alexandria, they simply nod to each other and start carving up an attacking group of walkers. His level in badass was so profound it ruined the "Where's Karl" meme because that question became about as foreboding as "where's Daryl".
Tara is an ex-police recruit who never passed the academy training course and is generally useless in combat (to the point that it takes The Governor having to teach her to use headshots on walkers because she and her sister didn't understand that body shots don't kill them, and she somehow sprains her ankle while running from walkers). Later, she finds some brief happiness after meeting Alisha, but suffers through a Despair Event Horizon after the prison falls, Alisha is shot by Lizzie and her sister is overrun by walkers. However, when Glenn finds her in the ruins of the prison and asks her to help him find Maggie, she takes an immediate level and starts headshotting walkers one-handed while escaping the prison, takes out several walkers by herself in the episode afterwards and becomes a member of a three-person power trio with Glenn and Noah in Alexandria.
Beth was so underused in the second season that she was practically Out of Focus, and her one memorable episode in said season had her attempting suicide after believing that living in the current world was pointless. By the time season 3 rolls around, however, she's much more capable with a gun and knife, and effortlessly dispatches walkers through the fence. When her father is killed in "Too Far Gone", she immediately opens fire on The Governor's troops, and later gets several badass moments in "Slabtown" and "Coda". However, she dies at the end of the former.
Andrea starts out as nothing more than a lucky survivor with no combat skills, and by the end of the first season is outright suicidal. Over the course of the second season she trains hard and refuses to join the other women in the kitchen. By the midpoint of the season, she's wading in to kill zombies with agricultural tools. By the finale, when she gets abandoned in the middle of a horde of walkers, she is able to keep running and scoring headshots all night, and after she runs out of ammunition is still killing them hand-to-hand.
Eugene starts out as a nerdy and cowardly Non-Action Guy who has to rely on his companions for protection. The only reason he's still alive is that he lied about knowing the cure for the plague so that people would act like his bodyguards. In "Self Help" he starts to involve himself in fights against walkers and he slowly grows more confident afterwards. He begins training with weapons and before the end of the sixth season, he has killed quite a few walkers. And he gets a few other awesome moments like biting his captor on the crotch so he can escape.
The Wire: Michael gets trained as a "soldier" (a hitman) for Marlo Stanfield's gang. Unlike most examples of this trope, this one is played tragically, and is meant to show how children in ghettos can be coerced into lives of violence.
Definitely Justin. In The Movie, he saves Alex and Harper (while taking a moment to give off a well-deserved Smug Snake vibe), kicks ass windsurfing, nails the Sixth Ranger of the plot with magical blasts without even trying, does some adventuring that (with his brains) slips him into Adventurer Archaeologist territory, and throws down during the family wizarding competition like a true badass - a competition that later on, he's sure to win (having gone through a personal mix of Crazy-Prepared and Charles Atlas Superpower in his training). One can only hope that they won't hit the Reset Button on him - but it is Disney, so Status Quo Is God.
Even before The Movie, he has already gotten Alex out of trouble countless times, in spite of her crappy attitude towards him.
Xena: Warrior Princess: A long-term-development example: Gabrielle starts the series off as a young, plucky, story teller, farm girl. Over the course of six seasons, she takes multiple levels, and develops her fighting skills until she's almost on a par with Xena, effectivley going from this◊. To this◊. Culminating in the Season 6 finale, when she becomes one of 3 people other than Xena to catch the Chakram and, in the last ever scene of the show, appears to be taking up Xena's legacy as a full blown hero.
The X-Files: Skinner took a level up in badass when he beat up Mr. X in the elevator. Don't mess with 'Nam vets.
Then there was his complete and utter owning of Cancer Man:
CSM: Listen to me— Skinner: No, you listen to me, you son of a bitch! This is the part where you pucker up and kiss my ass!
Top Gear: Specifically, it's "Took a Level in Badass Driving". James May was originally viewed as a joke, with his slow driving speed and No Sense of Direction. Over time, however, he has taken tutorage from two different Formula One drivers and taken power laps with the Stig. Consequently, he has become considerably better at fast-driving. Best shown in the second US special, where James was easily capable of keeping up with Jeremy on a winding mountain road somewhere in Nevada, even though Jeremy was established as the best driver on the show AND had a more powerful car. Cue Jeremy's befuddled reaction:
Jeremy: "What's gotten into him!?"
James: "Try 'n keep up, Jezza!"
Jeremy: "He is really shifting now, Captain Slow!"