Gohan from Dragon Ball Z. He has the potential to become the strongest person in the universe, but he hates watching people get hurt. The only reason he fights is for self-defense, or for the defense of others.
His father Goku isn't quite as pacifistic: he quite enjoys fighting. However, he does not enjoy causing pain or hurting people; he likes fighting as a sport. Hurting innocents is an excellent way to get him really mad at you. He also goes farther into Super Saiyan form than anyone else, and he isn't nearly as pacifistic when he's transformed.
Parodied with Amelia's father Prince Phil in Slayers. He is a passionate devotee to the concept of justice who greatly prefers to try and settle things with peaceful discussion, but is not only very savage-looking (he's been described as resembling a dwarf built to the scale of an ogre, and Lina Inverse mistook him for a bandit chief when she first saw him) but also prone to leaping headfirst into the fray with aggressive wrestling and kung fu moves that he gives goofy names. “PACIFIST CRUSH!” “GOODWILL TO ALL MANKIND KICK!” In fact, he's so strong a fighter he once managed to kill a demon with his bare hands. Amelia normally specializes in White Magic and Shamanist magic but she's quite willing to get physical when she feels inclined (one of her homebrew spells, the Visfanrank, actually equips her with magical boxing gloves for punching out demons.) She's usually too aggressive to count as a Martial Pacifist, though she does pull it off on occasion.
Kenshin Himura from Rurouni Kenshin, who was once a ruthless assassin, uses a reverse-blade sword because of his oath not to kill people again. When villains go too far, Kenshin's Battousai mode takes control, and he drops all traces of pacifism—although he's always managed to avoid actually killing someone even then.
Balsa from Seirei no Moribito. In fact, she's sworn an oath never to take a life and has a near-Heroic BSOD on one occasion where she thought she'd violated it.
While she might not exactly be a martial artist, the title character of Magical Girl Lyrical Nanoha counts to a certain degree. While Nanoha has become infamous for her method of making friends, it's worth noting that Nanoha always tries to solve conflicts through dialogue. Unfortunately, her enemies always insist on more violent means and when the chips are down, Nanoha doesn't pull any punches.
Toki of Fist of the North Star, the only one of the Hokuto Shinken brothers who doesn't make a point of going around and punching people in the face. Instead, he works as a wandering doctor, using his knowledge of Hokuto Shinken to heal the sick and wounded. When he does fight, Toki is strong enough to go toe-to-toe with Big Bad Raoh, all the while suffering from a terminal illness. He also has a technique that allows him to kill people without even touching them: it causes them to feel incredibly blissful, but also forces their body to contort in horrifying ways before they explode.
Haru Glory, in the manga Rave Master believes that Rousseau Was Right and that people shouldn't fight each other, and only goes into battle reluctantly. However, given that he's The Hero of an action-heavy manga spanning upwards of thirty volumes, he's reluctantly forced to go into battle quite often. He still somehow manages not to kill any of his opponents, although some of them die soon after defeat anyway...
Hiroki Sugimura of Battle Royale manga. He may look intimidating as he is the tallest boy in the class and is a kung-fu master, but he is actually a shy and gentle boy who dislikes to use violence unless it is his last resort.
Quatre Raberba Winner from Gundam Wing is similar. His first appearance has him telling his enemies to surrender, only attacking when they refuse to listen. That's how he wins Trowa's trust in their first encounter. He also praises Zechs and Noin in Endless Waltz for defeating so many of Mariemaia's soldiers without killing them.
He did against the toad hermit in the anime. He seems like an efficient pressure-point fighter.
Sir Bismark Waldstein aka the Knight of One might be the most powerful of the Knights of Rounds, but he openly says that he's not thrilled to use his impressive fighting skills unless it's really needed and that he views mere unrestrained violence as ignoble and unworthy.
Lynn Kylie/Kaifun from Macross is a very skilled and handsome martial artist, but in his conversations with Rick/Hikaru and Lisa/Misa he states his disdain for the military. However, despite him not going around and picking fights, he's shown as quite the Jerk Ass too, specially to his cousin and protegée Minmay...
Sora Wo Kakeru Shoujo has freaking ASIMO who knows kung fu but wants to be friends with everyone due to prolonged contact with Sakura.
Bleach has several. Kyoraku Shunsui and Hisagi Shuuhei are the most obvious examples, and Kira Izuru may qualify as well, though with overtones of Reluctant Warrior. Kaname Tousen tries to portray himself as this, but considering he cut off Grimmjow's arm to stop him from causing any more trouble he's not fooling anyone.
His suggestion that "Killing without purpose is only murder. But killing with purpose... is justice!" also seems to suggest that he's less averse to violence than he initially seems.
And really, crippling someone as violent as Grimmjow seems like a pretty good way to decrease bloodshed.
Chad is also something of an example.
In Naruto the kind, gentle Hinata Hyuga dislikes fighting and tries to avoid it when she can, but fights surprisingly hard if she has no other choice, especially if Naruto, the boy she loves, is involved.
Also, Shikamaru tends to dislike fighting and tries to avoid anything "troublesome". He even dubbed himself the "number one coward" because of this. However, he is willing to put his life on the line when duty calls.
Uchiha Itachi, the resident Aloof Big Brother who ran a Zero Approval Gambit (including, but not limited to slaughtering his entire clan, mind raping his own little brother on several occasions, joining an evil organization in order to keep his village safe, and just acting like an all-around dick) and committed suicide by little brother in an attempt to keep the peace, never gets into a fight if he can avoid it, despite his disgusting amount of skill.
This is pretty much the defining character trait of Kenichi Shirahama from Kenichi: The Mightiest Disciple. A peaceful young man who only took up martial arts to stop being bullied, he often tries to talk his way out of fights first, and will even walk away from those who challenge him, only resorting to violence if he has no other choice (or if a challenger calls him a coward).
Also, several of his masters. None of them will actually kill you (well, Apachai might do it accidentally) but Akisame and Ma Kensei are the most notable.
After the Ragnarok arc, the conflict between the Martial Pacifist principle (katsujinken - "life saving fist") and the opposing principle (satsujinken - "killing fist") becomes the main plot line. The organization of evil satsujinken mentors, Yami, believes that Martial Pacifists actually degrade martial arts by making them less "martial".
Yellow of Pokémon Special. Sweet-tempered and happy-go-lucky, she hates fighting so much that it pains her to fight her attackers, and sometimes even heals them afterward. Her first option when facing an enemy is to run away. She even tries to figure out ways to immobilize her opponents without actually hurting them. However, when push comes to shove, she will fight if she has no other choice and watch out, as she has the ability to make her normally low-leveled Pokemon to get abnormally stronger in a mere few seconds.
Parodied (like everything else) in Bobobo Bobobobo with Mr. BoJiggler, a fusionof Bobobo and Jelly Jiggler. He claims that he is a pacifist, and the villains are often quite willing to work out a peaceful solution to the issue at hand, but he still assaults them with super-powerful attacks while screaming things along the lines of "Why can't we just all be friends?"
Gintoki from Gintama once used to be a mighty warrior with the nickname "White Demon" who led the war against aliens' invading Japan. Nowadays, he is working as a free-lancer, willing to take in any odd jobs to pay the rent. Like the Kenshin example above, while he avoids using force and acts like an idiot from time to time, he will not hesitate to commence asskicking should the need arises.
Dove in The DCU. A pacifist martial artist, and probably the only serious pacifist superhero. He makes a point of actually never hurting anyone with his moves. Of course, since he associates with his brother, Hawk, who resorts to violence in most situations...
Shang-Chi, the Master of Kung Fu, of Marvel Comics, who faces opposition from his brother Moving Shadow.
Broot from The Omega Men is an odd subversion; while he prefers to use violence only as a last resort, he was exiled from his planet for his staunch belief that, yes, sometimes violence is the answer.
Although the Teen Titans' Raven has accepted that violence is necessary, she doesn't like it one bit.
Spider-Man is not a martial artist but once he grew up, he would normally try to talk his opponents down and then restrain them with webbing. Of course, talking rarely works and the webbing only works part of the time, resulting in a prolonged battle.
As of Spider Island, Pete has had some serious martial arts training enough to fight at the level he could before his spider sense was shut down previously, thus playing this trope straight.
Surprisingly, Sin City has one: Wallace. He is very polite and often asks to be left alone before having to pull out his Navy SEALS martial arts training. At one point, he is even seen meditating.
Superman of the DCU. Considering how greatly he out levels most of his opponents, yet adheres to a strict no kill code, most of his battles involve him lightly batting around opponents until they surrender. Even then, he goes out of his way to talk to his opponents before violence breaks out. He also ensures that no severe harm is endured by all but the very most evil of his foes.
In fact, most of the action in a Superman comic involve Superman simply getting in the way of the attempted kill strikes of villains who want to cause death and destruction for their own purposes. Only villains who really are as strong as Superman (or have a plan to attack him that doesn't involve physical force) typically exchange blows in a standard duke 'em out fashion. In fact, when one alien travelled to earth to battle Superman in order to prove his badassery, Supes allowed him to soundly kick his ass so that the alien would leave Earth alone after he finished gloating.
Ultimate Thor. He consistently attempts to reason with opponents, but can at the drop of a hat prove why he is known far and wide as the most powerful being in his universe (and several neighboring universes, as well).
Storm. Unless circumstances dictate otherwise, she will often be the first to offer a reasonable, peaceful solution. She tries her best to adhere to a strict "no-kill" code, and despite being one of the most powerfulX-Men on the roster, actively works to ensure that she does as little harm to her adversaries as possible. Of course, her tolerance does have its limits.
Curiously inverted in the French comic Dungeon: Marvin (a weapon-master and bipedal dragon) is a Person of Mass Destruction, but he is a stern adherent to a peculiar religion that (among other things) forbids him from ever attacking somebody who has insulted him. Unsurprisingly, having to endure verbal abuse from anybody who learns his weakness has made him a cranky, cranky fellow.
The popular Deva Series has Laura Sims who, despite having the sworn Thou Shalt Not Kill, is a subversion of the trope, preferring to talk after the defeating her opponent.
DC Nation has a few. Raven, as mentioned above. Hugh Fulbright, one of Earth's Blue Lanterns. Granola Girl Fauna. The Nation-verse Green Arrow Connor Hawke also follows this path, as he never abandoned his faith in this universe.
Sue Dibny(checking in with JLA members on patrol): "So business as usual?"''
Connor:"The usual, though we should always work..." There's the sing of a bowstring over the com. "To put ourselves out of business."
Kyon from Kyon Big Damn Hero. He explicitly states that violence is the last resort, but sometimes it is required. He also has the skills and training of a few black belts.
The Jedi from Star Wars, especially Obi-Wan in A New Hope and Luke by the end of Return of the Jedi. In The Empire Strikes Back, Yoda points out that Martial Pacifism is an inherent part of being a Jedi.
Yoda: A Jedi uses the Force for knowledge and defense, never for attack.
Qui-Gon in episode one was the epitome of this, especially when his mid-battle meditation contrasted against Darth Maul's animalistic, restless pacing while the two were separated by a forcefield. Luke would provide a similar contrast with Darth Vader in Return of the Jedi, with Luke constantly turning off his lightsaber unless he was being directly attacked.
Mr. Miyagi of The Karate Kid, who opposes the brutal Cobra Kai dojo. He is very insistent on attempting to solve Daniel's problem peacefully through dialogue, and only when he sees that this will not work does he agree to a fight (in a relatively safe venue: a martial arts tournament). Even then, he stresses that the point of the fight is not to punish Daniel's tormentors, nor to get revenge. The point is to earn their respect, so that they will stop bullying him.
Wong Fei-Hung, a Chinese folk hero who has been the subject of more movies than can be counted was one of these characters, particularly in Jet Li's Once Upon a Time in China series.
The main character (Sing) at the end of Kung Fu Hustle becomes an example of this trope, as he opens a candy shop as opposed to, say, teaching kung fu. He, too, faces an arrogant villain, the Beast.
The Big Bad from The Transporter 3 seems to honestly consider himself a pacifist. This does nothing to stop him from trying destroy half the Ukraine for no apparent reason or temper him when he tries to stab Frank to death.
Ip Man from the eponymous film, who refused the call to start a martial arts school and prefers to talk his opponents down. Of course, if pushed, he will fuck you up. He starts his martial arts school in the sequel, but still prefers to talk rather than fight, and hasn't lost any of his ass-kicking ability.
Dalton from Road House, who teaches his fellow bouncers to "be nice... until it's time to not be nice".
Played with in the Discworld novel Thief of Time with Lu-Tze: after he spends most of the book going out of his way to find peaceful solutions or facing potential opponents down with the power of his reputation, his sidekick Lobsang begins to suspect that he's avoiding combat because he can't fight very well any more. Lobsang is wrong.
Carrot Ironfoundersson would rather talk the situation down, but if he has to fight then he can punch out trolls and put a sword through a stone pillar.
Wedge Antilles is very willing to kill his enemies, typically Imperial. But he's much more reluctant about groups that aren't explicitly his enemies - he'll kill them if he has to, but he doesn't like it. In Starfighters of Adumar he infuriates the diplomatic liaison by refusing to kill the unskilled Proud Warrior Race Adumari in duels, thus making the Imperials, who do kill in duels, look stronger. Late in the book, when the liaison and much of Adumar has turned against him, he's death on wings, though.
As seen in Outbound Flight, Chiss as a people are isolationist, tending to ignore most things going on outside of their borders. They don't even trade much with outsiders. If someone does attack them, they wipe the enemy out, but they wait for that first attack. The Chiss language has no phrase for "preemptive strike", and they find the concept unlawful. This makes Commander Mitth'raw'nuruodo very unusual. He tries to convince his brother that it's foolhardy to let their enemies choose the time and place to strike, and eventually launches several attacks that get him exiled from Chiss territory.
In Survivor's Quest, Luke is shown the Redoubt, a star cluster that is more or less the last refuge of the Chiss people, should their military fall to something. Luke idly comments that with a sanctuary like this, the Chiss can afford to let their enemies take the first shot. Chaf'orm'bintrano takes offense to this.
"That has nothing to do with the Redoubt. It is completely and purely a matter of honor and morality. The Chiss are never to be the aggressor people. We cannot and will not make war against any until and unless we have been attacked. That has been our law for a thousand years, Master Skywalker, and we will not bend from it."
Of course, once the Chiss have actually been attacked, they have no problem with abandoning the defensive strategy. In fact, they're really skilled and ruthless when it comes to war.
Chiss law could be seen as, "Never throw the first punch, always throw the last punch." They'll deal with you peacefully if they can, but if you attack them, they can end you.
As already stated above, Luke himself is a Martial Pacifist of the highest order; he really doesn't like fighting, and will avoid it whenever possible. If he's forced to fight...well, the only thing you can do is pray to the Force. It's clearly illustrated in Heir to the Empire. During his first encounter with the Noghri, seven of them advance on him at once, brandishing unknown weapons and trying to herd him to some unknown destination. He tries to talk his way out, he tries to trick his way out, he considers running and sees that won't work - but when he sees there is no other way he feels sorrowful and kills them all within seconds.
In the Anita Blake series, Richard is introduced as a Martial Pacifist even in the face of not only his foes mocking him for it, but also the Mary Sue protagonist. Like all the werewolves he possesses superhuman strength and regenerative healing; unlike the others he lifts weights and trains in martial arts so he won't have to kill. The result is a stalemate in the first few books between himself and Bad Boss Marcus, with Anita criticizing him for refusing to kill him in their next confrontation. Of course, when Richard finally listens to Anita, she promptly flees in terror and jumps into Jean Claude's arms. Apparently vampires are better than werewolves, because they're more fastidious about their people eating.
Atticus Finch, from To Kill a Mockingbird. His children's hot tempers and constant scrapping are an aggravation to him, and he has no interest in having his honour defended. He believes in the law, and his courtroom manner is polite and gracious even to opposing witnesses who are clearly hostile towards him. Also, he can kill a charging rabid dog with one shot right between the eyes (maybe a little to the right) because the sheriff doesn't think he can make the shot at that distance. Note that this means that with a mad dog charging towards him and his children, his hands don't shake in the slightest.
Sisterhood Series by Fern Michaels: Yoko Akia is very much this. She is usually calm and peaceful. However, she beat Harry Wong, the second greatest martial artist in the world and Arrogant Kung-Fu Guy, in a sparring match before going out on a date with him. Indeed, no one in the series has been able to beat her in a fight! In other words, do not get on her bad side if you know what's good for you!
The Hunger Games: Peeta Mellark. He can kill when he has to but is more or less a pacifist who doesn't want to see more blood shed, even after participating in two Hunger Games. Katniss has aspects of this as well but also has a streak of "means justify the ends" that lands her with a much higher body count than Peeta.
The Council of Lords from The First Chronicles of Thomas Covenant have all sworn the Oath of Peace which while it doesn't stop them from using violence it does limit them to the absolute minimum level of violence necessary.
Do not hurt where holding is enough;
do not wound where hurting is enough;
do not maim where wounding is enough;
do not kill where maiming is enough;
the greatest warrior is he who does not need to kill.
Comes back to bite them when they find out this is why the Old Lords were so much more powerful - the Oath is inhibiting their magical abilities because said magic is potentially destructive. Even after learning this they decide to keep the Oath as they think it's too important a principle to abandon.
Tavi Calderon of Codex Alera is notable for this even with Always Chaotic Evilbugs. In the long run, it's a remarkably good strategy, assembling the ragtag team of species that finally halt the Vord advance.
Phenix detests fighting people and won’t do it unless someone he cares about is being threatened, and even then will try to find a peaceful solution first. If he can’t find one though, watch out.
North is an odd example, being a cross between this and a Blood Knight. He, like Phenix, doesn’t believe in violence as a first solution and will try to find a peaceful way to resolve problems, but he has absolutely no patience or mercy for people he deems evil and will eliminate them on the spot, relishing the battle as he does so.
Trapped on Draconica: Princess Erowin goes on record by saying she detests violence of all kinds but that doesn't mean she'll refuse to fight in self-defense.
Live Action TV
The Doctor from Doctor Who. Although if the circumstances call for it, he is willing to kill. A lot.
Playfully parodied in The Middle Man. Dub-Dub describes herself as a pacifist but cheerfully beats others up with whatever weapon comes to hand should the need arise. Lacey is similar.
Juken Sentai Gekiranger has the seven Kensei, martial arts masters who have taken a vow not to fight. They now serve as mentors for the Rangers.
Gabrielle from Xena: Warrior Princess is a Martial Pacifist for a majority of the series. Violence is a second choice to talking, and killing someone is a huge deal for her, which she only does to protect others.
Babylon 5 has John Sheridan, war hero, the man who defied the First Ones and led the effort to throw them out, but who, when recording a message to his unborn child, started with the words his own father told him, "Never start a fight; always finish it."
Marshall from How I Met Your Mother. Shown to be a competent fighter, but only when he has to back-up one of his friends.
Star Trek centers around the United Federation Of Planets and their exploratory/defense force, Starfleet. Despite extolling the virtues of peace and cooperation, they are able to maintain a Balance of Power against the Romulan and Klingon Empires through much of the series history (even during a brief time when the Klingons and Romulans teamed up against the Federation). When push comes to shove, the Federation is quite capable of demonstrating why you must Beware the Nice Ones.
Believe it or not, Thor. In spite of his violent reputation, he was one of the few Gods who didn't take pleasure in war, and reserved his violent tendencies for defending the gods from Jotnar.
Freyr from the same mythology. He is the god of peace and his followers avoided fighting, but in two myths he was forced to fight.
Teacher: The only use of Ti Kwan Leep is self-defense. Do you know who said that? Ki Lo Ni, the great teacher.
Ed Gruberman: Yeah? Well, the best defense is a good offense. You know who said that? Mel, the cook on Alice.
The various "Sacred Vow" Feats from the Dungeons & Dragons 3.5 supplement, The Book of Exalted Deeds tend to end up this way. They forsake an earthly vice (such as sex, drugs, or violence) in order to gain massive bonuses both to resist it and to seek an alternate path. For example, a Monk who has taken Vow of Poverty, Vow of Peace, and Vow of Nonviolence is an absolutely terrifying combatant, provided he only deal nonlethal damage (which all his Vows allow).
Argagarg from the Fantasy Strike games. His attitude is shown most clearly in Flash Duel, where he wins a round if it ends without anyone getting hit.
The Children of Gaia from Werewolf: The Apocalypse have a reputation in-game as hippies, and it's not entirely unearned; of all the tribes of the Garou Nation, they're the ones most likely to try and convince other Garou to look deeper into the issue, examine all the sides, and maybe find a non-violent resolution if possible. They're still warriors for Gaia, and also the ones who know that if no peaceful means of resolution is possible, then it's time to go absolutely rip-shit.
Invoked by users of the Subtle Force external art in Legends Of The Wulin. They don't have to be pacifists; they can choose to cause long-term harm with their strikes. However, the style provides a damage bonus when dealing wounds that will heal after a good night's rest, a technique that causes aggressive opponents to suffer, and another that allows Marvels (such as tripping or dizzying) in place of your primary attack.
In Jade Empire most followers of the way of the Open Palm, including, potentially, the player character. Emphasis on "most"; the Way of the Open Palm is not necessarily good, just as the Way of the Closed Fist is not necessarily evil, or so the developers would have us believe. It's a popular theory that the Big Bad, a man obssessed with things being in their proper place, is a follower of the Open Palm.
The Shaolin monk Chinnen from Power Instinct is an intentional subversion, being a selfish know it all who's likely to pound you for looking at him the wrong way. His idea of meditating is passing out after binge drinking.
Lynn Baker from Rage of the Dragons. She's one of the types who practices martial arts as a means of spiritual fulfillment and all that.
Elias, a Catholic priest from Rage of the Dragons and Power Instinct Matrimelee, as well. While he abhors violence in general, he recognizes that there are times when there is no other alternative, and that the Father will understand and forgive.
Liu Kang from Mortal Kombat can be an example. Despite the copious gore in the games' fatalities, Liu Kang is the only character with a fatality that isn't actually fatal, because of his time with the Shaolin having taught him peace.
Only in the first game, however. Starting from the second game on, he doesn't seem to have an issue with turning into a giant dragon and biting peoples' torsos off.
He still gets a non-fatal Fatality in the second game. It's business as usual from the third one on though.
Kim Kaphwan of the Fatal Fury and King of Fighters series is an extremely amicable Tae Kwan Do master who is working to rehabilitate recidivist criminals Chang Koehan and Choi Bounge with burning justice. His son Jae Hoon hopes to follow in his footsteps, and it doing a fair job.
Hotaru Futaba, also from the Fatal Fury series, is a prime example. A calm, joyful girl, and overall a very sweet person. Fighting is, for her, the only way she knows how to reach her beloved brother Gato.
Boman Delgado of the Rival Schools series firmly believes that violence is not the answer as a devout Christian, but he's prepared to do whatever it takes to bring peace to his school.
Dhalsim from Street Fighter. He only enters the tournament for the purpose of raising money for his village and is deeply troubled by the fact that he has to resort to violence in the process. Even when fighting, he goes out of his way to avoid causing serious harm to his opponents.
Also, Elena. A Capoeira face-kicking beauty who travels the world and enters fighting Tournaments to meet new friends. Seriously.
Ryu, perhaps? He's probably more fight-happy than average but the rest fits.
Arguably, these are all explained by the Street Fighter tournament being, at its very base, a sporting event. It is, after all, a tournament, and the people in it are doing so on a voluntary basis. (Or mostly voluntary.) Fighting for sport against an opponent who is also doing so can probably still fill a pacifist ideal.
Gouken is perfect example of this trope, contrasting his Arrogant Kung-Fu Guy brother Akuma. Although both of them studied the same master, Goutetsu, Gouken despised killing so much he toned the lethality in his fighting style down, which he then taught to Ryu and Ken. Despite not embracing the Satsui no Hadou like Akuma, he was still powerful enough to beat Akuma in their first encounter, and survived Shun Goku Satsu in their second. He has even achieved a level of Mu no Ken (Fist of Nothingness) that is on par with Akuma's Satsui no Hadou, yet completely opposite in nature.
Kindly priest Tiger from Martial Masters, who prays before and after matches and asks his opponent for forgiveness after defeating them.
Yakuza 's Kazuma Kiryu would much prefer to live a peaceful life tending to an orphanage and taking care of children than having to fight. When push comes to shove, though, make no mistake: he will absolutely kick your ass. And if you hurt a kid in front of him, don't bother fighting back: you'd be better served to pray he doesn't just straight-up kill you.
In the Mass Effect series, Shepard is this if you take the Paragon options (though its moral compass aligns more to 'reconciliation vs aggression' than 'good vs evil'). S/he leaves a swath of devastation through anyone who won't talk, but once s/he get's you in dialog, a peaceful resolution is almost always possible. If you really focus on pacifism, you can actually even talk down Saren at the end though it only gets rid of the first stage of the end boss, because the Reaper then proceeds to possess him.
A lot of background dialogue implies this is why many races are wary of Humanity. Their first contact with the rest of the galaxy came in the form of a short and bitter war against the Turians (who admittedly fired first) before the ceasefire was eventually called; only to take everyone by surprise by coming onto the galactic scene under a banner of peace. Many find it hard to reconcile human expansionism and brute military strength, with their diplomatic flair and desire for a greater role in protecting galactic peace.
Assassin Ansaksie from Iji has elements of this. She will avoid killing people if she doesn't feel it's necessary (such as Iosa knowing too much), but when it's time to kill, she has her Massacre handy.
Iji herself can also qualify if you play that way. One of the enemy logs wonders at the fact that the "human anomaly" appears to be unstoppable, to the point where she can simply walk past hundreds of troops and through a hail of gunfire without even bothering to fight back.
One of the warrior trainers in Planescape: Torment is a monk whose order trains in preparation for the battle of the apocalypse. Except in cases of calm, controlled sparring, they are strictly pacifistic. Thus he gets his sacred beads stolen by a band of common thugs and enlists you to get them back. Whether 'you' go about it peacefully is your choice.
In fact, the monk will be happier if you tell him that you did use violence to get the beads back (regardless of whether you're telling the truth or not). The Nameless one can fit into this trope as well, as the game often gives the option of not fighting, and frequently rewards you better if you manage to avoid combat.
General Hawthorne of the Alliance in World of Warcraft strongly believed in winning the war with minimal casualties, focusing more on breaking the fighting spirit of the Horde than wiping them out. Unfortunately, the Alliance ambassador wanted to wipe them out, and the Horde rather conveniently learned when to ambush Hawthorne.
In Fallout: New Vegas, the Courier can be played this way. If you specialise in speech, you can talk nearly anyone down, despite being capable of destroying them in a matter of seconds.
Star Trek Online's Deferi have this as their racial hat. They are neutral in most of the game's conflicts due to their ethical code and philosophy of seeking balance in all things and will only fight in self-defense. At the time of the game they're at war with the Breen for attacking them in ancient times, and with the Borg because they're a threat to everybody and can't be negotiated with for the most part.
The Goners of the X-Universe are Actual Pacifists for the most part (their ships aren't even armed, in a universe where even civilian freighters carry at least a tail gun), but push them far enough collectively and they will fight back with lethal force. This is amply demonstrated at the end of the Goner plot in X3: Terran Conflict when the Goners have the player character smuggle a crapload of bombs onto a pirate space station whose residents have been preying on their supply lines.
In Final Fantasy X-2, a game-long sidequest has you trying to convince the Ronso not to go on a Roaring Rampage of Revenge against the Guado (Seymour Guado had committed genocide of most of the Ronso in the previous game). Given their size and Proud Warrior Race Guy tendencies, this is easier said than done. If the sidequest is completed, the final cutscene of the quest has the Ronso arguing over whether or not to kill the Guado, before calling it off and coming to the conclusion that true strength is not strength in battle, but rather, "strength to avoid battle."
Humanity is this in the Galactic Civilizations series. They specialize in diplomacy, and as such the Drengin Empire persuaded another race to invade them. Humanity fought back and kicked the attacking species' ass, terrifying the Drengin.
Dhiar from the mature satire Incubus Tales comports himself as a pacifist in all circumstances possible and always tries to resolve a situation without violence; he has, however, had to resort to violence more than once and carries a whip — with which he is highly skilled — as a matter of pragmatism.
The unnamed heroine of The Bully's Bully tries to deal with bullies nonviolently if possible and with minimum violence otherwise.
The heroic Dove from the ''Global Guardians PBEM Universe is a Martial Pacifist who specializes in evasion, blocking, and misdirection in combat. He's an expert at somehow finding convenient trees, walls, cars, and so on to duck behind just as the bad guys attack. He only goes "offensive" when he absolutely has to.
Corrie, Cambria, Phylis, and Spark from The Gungan Council would all wish not to harm another being, yet they're all ready to kick ass when needed.
This is part of the philosophy of the Air Nomads. Aang lives up to this, except when in the Avatar State; in fact, a minor plotline in the last season revolves around the question of whether he could set aside his pacifism and kill Ozai. He took a third option.
Samurai Jack himself was taught this from an early age by many cultures, including the Shaolin monks.
In fact, Jack is quick to draw the blade against opponents, who are invariably robots. The few that are not robots, however, he hesitates. In one episode, his readiness to fight gets him in trouble when Aku uses his anger to create Mad Jack, a clone of Jack that knows only anger. As they fight, Jack begins to look more like Mad Jack, until it's almost impossible to tell them apart (and they set the whole forest on fire). Jack is only able to defeat Mad Jack by meditating to restore his inner calm, which results in Mad Jack vanishing. Jack is noticeablyslower to anger in subsequent episodes as a result.
Jackie Chan from Jackie Chan Adventures is something of a variation of this trope, though less on the disciplined side. While constantly saying he doesn't want to resort to violence... he tries to run away. Naturally, being Jackie Chan, it's used for a comedic edge and he will end up fighting. And he has every reason to!
Parodied in Futurama episode "Godfellas". The Monks of Teshuva try to bluff Leela and Fry with their martial arts skills; but when Leela calls their bluff, they immediately back down and admit to being Actual Pacifists.
Legend Of The Dragon has Ang as this. He thinks about responsibility instead of power, prefers to think before acting, and he felt his sister Ling deserved to be the Golden Dragon. Well, guest what? He was chosen to be the Golden Dragon instead of her! He does prove to be quite the fighter when he has to be.
The Shaolin Monks studied and developed their fighting style out of self-defense and swore an oath to only use these arts to protect. They took no pride in killing, and even less in needing to fight in the first place.
The entire martial art of Aikido is based on this principle. It has no purely aggressive moves.
Many people believe eastern martial arts started in India by Buddhist monks as a way to discipline body and mind, not for fighting.
The main alternative theory is that it was because weapons were more expensive than most could afford and banned by many governments.
The art of Taijiquan (more commonly known as Tai Chi Chuan) is both a healing art and a martial art, though it's not clear which (if either) it started as. Its positions and motion help one to improve strength, endurance, flexibility, balance, co-ordination, and patience - and, like all arts, it has a philosophical element that emphasises knowledge of the workings of one's mind and living in the moment. However, all the moves/forms have hand-to-hand combat applications (albeit sped up, of course, as Taijiquan is usually practiced at a firm but relatively slow pace). More specifically Taijiquan teaches one to avoid superfulous movement and use the attacks of others against them - not by delivering counter-blows to stop their attacks dead, as in Kung Fu, but by moving with one's opponent and thereby putting them off-blance. Philosophically, Taijiquan is supposed to teach its practioners to resolve/avoid cognitive dissonance (i.e. wholeheartedly believing in two contradictory concepts at once), deal with others in a social context (including duels of wit), and just generally move less clumsily and with more grace.
There's a joke that goes like this. Also told about Israelis, and probably others.
An Englishman, a Frenchmen, and an Russian are traveling through the jungle when they're captured by cannibals. The cannibal chief is a civilized person, and will grant them one last request. The Frenchman asks that he have sex with the chief's daughter before he dies. The chief grants this, the Frenchman does the horizontal mambo, and is killed and cut up for stew. The Russian asks that the chief kick him in the ass. The chief is confused, but willing, and does so. The Russian tumbles, comes to his feet, and pulls out a pistol. He shoots the chief and a half a dozen men, then runs for his bag, pulls out a rifle and massacres the rest of the cannibals. The Englishman is shocked. "Why", he asks the Russian, "did he not do that earlier?" The Russian sneers and says "Russians are not aggressors."
The Israeli version changes the punchline to, "And get blamed by the UN for being the aggressor?"
There's an old joke about a Quaker in Philadelphia who confronts a burglar on his front steps with a double-barreled shotgun, and tells him "Friend, I mean thee no harm, but thou art standing where I am about to fire!"
Guillaume Henri Dufour. He was General of the Swiss army during the brief civil war, which he won with less than 100 dead on both sides combined. Later, he was instrumental in founding the Red Cross and presided over the first Geneva Convention. He was also an important topographer, leading to Switzerland's highest peak being named after him.
Perhaps unbelievably considering his reputation, Sun-Tzu considered that the greatest victory of all was one where the fight never happened.
He explains it himself. An enemy will only fight if he believes he either has a chance to win, or you've backed him into a corner and he's fighting for his life. A completely crushing victory provides an enemy with neither. Also, convincing an enemy to surrender without a fight gives you an opportunity to preserve his resources intact for the next fight.
In his own words:
Hence to fight and conquer in all your battles is not supreme excellence; supreme excellence consists in breaking the enemy's resistance without fighting.
Chuck Norris, as a rule, prefers to back down from petty conflicts - possibly because he's a Christian who takes turning the other cheek seriously.
He tells a story in his autobiography(?) in which he's at a bar, and a biker-type comes up behind him and insists on taking his seat. Chuck complies without saying a word. Shortly thereafter, the biker realizes that he just took Chuck Norris' seat. He walks over to Chuck, now sitting in a booth and asks why Chuck didn't simply beat him up. Chuck's reply: "What would it prove?"
Allegedly beat up some (armed) would-be robbers who knew who he was.
Gichin Funakoshi was the founder of modern karate. He recounts in his autobiography how, in the chaos of post-war Japan (when he was in his seventies), someone tried to mug him. In Funakoshi's memorable phrase 'his stance was full of holes', so Funakoshi stepped in and held the guy by the balls until the police arrived. He follows this story by a description of how ashamed he felt later, considering that he had abused his art.
Jet Li has gone on record saying he's never been in a real life fight and hopes never to be in one and is strongly against the use of martial arts for violent ends. 
Any good martial arts teacher should emphasise to their students that their skills should only ever be used as a last resort if they are in physical danger.
Many professional armed forces tend towards this, as they recognize that not only is wanton and unnecessary slaughter bad PR, but it also can cause more problems than it solves. They also tend to have fairly specific rules for when lethal force is required, and will use it quite effectively once it is allowed. Leading to this somewhat dark take on the trope:
General James Mattis, USMC: Be polite, be professional, but have a plan to kill everybody you meet.
There are jokes that S.W.A.T stands for "Sit, Wait and Talk". That is because, despite dressing up like combat soldiers and packing more heat than a supernova, S.W.A.T teams are not there to kill suspects, but to intimidate them into surrendering. They will if they have to, but most see the best outcome being where nobody, including the suspect, dies and everyone comes back alive.
Brazilian MMA fighter Vitor Belfort was once asked on an interview what he would do if someone hit his car, to which he responded: "If someone hit Pavarotti's car, would he start singing an opera?"