Saint Seiya has Andromeda Shun, who after four seasons and at least three movies refuses to give up on the idea of non-violently settling problems, and talking to his enemies in the hopes of reasoning with them. He has the unfortunate tendency to combine this noble character with Martyr Without a Cause and almost giving away his life on a few occasions... but when push comes to shove and the enemy proves they are a monster, he will fight and kill them if need be. To his credit, he's caused at least one Heel-Face Turn among his opponents, and held back and throttled a body stealing god through sheer love of peace.
Goku from Dragon Ball is this (especially the horrible judge of character part) seeing as how he loves to fight but never sets out to kill, even when he is forced to. He actually has the lowest body count in the series, on important characters at least, lest we forget the time he went on a Roaring Rampage of Revenge and destroyed the entire Red Ribbon Army when he was a kid (though they DID piss him off really badly by killing Upa's dad, among other deeds). And of course, he kills plenty of people in the movies, though those aren't canon.
Gohan is another great example especially in the Cell Saga, before Goku dies at least. Gohan refuses to get mad enough to blindly kill Cell in Roaring Rampage of Revenge because he doesn't want to kill anyone. It takes Android 16 deathbed speech about how it is okay to kill to protect the innocent and then subsequent death at Cell's hand to get Gohan to let it loose.
Haku of Naruto hated fighting and killing, but also desired nothing more than to see Zabuza's wishes fulfilled. In his final battle, despite having many opportunities to do so, he never struck a fatal point with his senbon despite it significantly extending the battle.
In Freezing, Kathy Lockhearte is a sweet, rather meek girl who wants to one day become a novelist and raise a loving family. Too bad for her that she naturally possesses the potential to become the one of the most powerful Pandoras on the planet, and her Jerk Ass father constantly pressured her into becoming the "world's savior" more for to boost his own political career than to actually, well, save the world.
Simon from Gurren Lagann starts out as one of these. He's only content with working as a miner and isn't happy with Kamina sending him on adventures. Then Kamina dies, leaving him to fend for himself, and by the end he's piloting a mecha capable of punching another mecha into an alternate dimension, where it explodes. Which it does.
Raiden is one of the Lightsworn’s big guns in Yu-Gi-Oh!. He has gone behind enemy lines and taken out plenty of enemy commanders. However, beneath these actions lie his wish for peace, his desire for a swiftly put an end to the conflict.
Superman tends to try talking things out before resorting to violence, even if it seems clear that the enemy cannot possibly be talked down. Being Nigh Invulnerable helps with this sort of philosophy.
DC Comics' western character Bat Lash. He's a fairly cheerful Reluctant Warrior, though, who doesn't anguish much about beating up villains, instead maintaining a steady stream of banter about how he did try to avoid a confrontation, and, really, all he wants is to be about his business, but they've forced the issue. And he means it.
Most of the Autobots in the Transformers franchise don't want to be warriors. Makes sense since most of them were built for civilian purposes. Optimus Prime in particular always has humble origins: dock worker, data clerk, desk jockey police officer, etc. In all adaptations except Transformers Animated where he's a washout cadet who mistakenly thinks War Is Glorious (this ends after his first taste of real war with the Decepticons) he hates war and only fights because the Decepticons have to be stopped no matter the cost. In Transformers: Robots In Disguise he takes advantage of an opportunity to leave Cybertron and explore the universe so he can abandon his identity as "Optimus Prime" forever and rediscover "Orion Pax".
It is implied in Racer and the Geek that most mercenaries only choose that line of work after exhausting all other options. However, coming to enjoy it is not unheard of.
Ditto his mentor, Mr. Miyagi. "Fighting always last resort."
The Guns of Navarone: Corporal Miller. He's seen one too many examples of the human cost of the war.
Miller : "Well, right now I say to hell with the job! I've been on a hundred jobs and not one of them's altered the course of the war! I don't care about the war anymore, I care about Roy!"
Brother Gilbert in Dragonheart had a minor dose of this trope. He agreed to fight against Einon because he was so evil, but kept his shots non-fatal. Then, when he was presented with Einon himself as a target, he drew a bead on the tyrant's heart but hesitated while growling out "Thou... shalt... not... kill..."
Star Wars series: Yoda. His's comment that "Wars not make one great!" was later elaborated upon with Form Zero, a sort of Jedi philosophy that stressed the importance of finding a non-violent solution to problems.
In Epic Nod quits the Leafmen because he doesn't play well as part of a team, preferring doing things his way.
Over the Wine-Dark Sea: Menedemos and Sostratos; while they constantly have to defend themselves against pirates, warlords, and assorted blackguards they prefer to avoid a fight. In their case it is less from idealism and more because it interferes with their primary mission
Sam Temple in Gone doesn't want to step up and become the leader of the FAYZ. In fact, he doesn't at first, letting Orc, and later Caine, take over. Only when he sees how evil Caine is does he finally take charge.
Leland de Laal in Helm doesn't like fighting or, especially, killing, and avoids it assiduously wherever he can, even after being made the captain of a unit of mounted infantry. Up to and including engineering a peace treaty with the nation his unit was originally formed to fight.
In Alan Dean Foster's The Damned, every soldier in the Weave is this. Most of the Weave races abhor even the thought of violence, and the ones that can bring themselves to fight do so with much distaste. Their foes, the psychic influence-wielding Amplitur, do not like to fight either, but their fanatical belief in uniting all species beneath the banner of "The Purpose" drives them to do so, and they don't hesitate in genetically modifying species under their rule in order to make them better fighters. The only species that enjoys fighting is humanity. The Weave manages to recruit humankind, and the only thing that frightens them more than having humans as allies is the possibility of humans falling under the Amplitur's control.
Yuri Zhivago of Doctor Zhivago is conscripted into the Imperial Russian Army and later the Red Army as a medic, but in the latter case, he is forced to take up a gun when the Reds are cornered in a Siberian forest by the Whites. Upon seeing that most of the White soldiers are still pretty much schoolboys, he instead shoots at a tree to make it seem to his commanders that he is helping in the fight without actually killing anyone, but to his horror, some of the White soldiers still end up in his firing line in the hustle and bustle of the charge.
Live Action TV
Buffy the Vampire Slayer: Buffy is very much one, especially during the high school seasons. Giles has to do everything short of grabbing her by the hair.
Stargate SG-1: Daniel Jackson often has to reconcile his idealist ways with the more pragmatic ways of his friends. Sometimes he wins, sometimes they do, depending on the episode.
Alias Smith and Jones: Even as outlaws, Heyes and Curry both fit this trope. Their whole modus operandi for train- and bank- robbing is to secure the maximum amount of loot with no casualties whatsoever. Kid Curry seems unlikely as a Reluctant Warrior, but although he is a Gunslinger par excellence, he really, really, really doesn't want to shoot anyone. The rationale for his becoming a phenomenally fast draw is that the faster he can draw the gun, the less likely the chance that he'll actually have to fire it. And the only two times he DOES actually shoot someone are when they draw on him first, and even in those circumstances he hates having been placed in that position.
Doctor Who: Before the Last Great Time War, the Doctor was a Science Hero for whom lethal force was the last resort but still a valid one. After the war...he still is. During the war, on the other hand, he fought on the front line until he had no option but nuking both sides to save the rest of the universe. Expanded on near the end of Eleven's run - it turns out Eight initially refused to fight and just helped those caught in the crossfire. When it became clear this couldn't last, he constructed a whole new persona that his other incarnations refuse to call "the Doctor".
Firefly: Both Dr. Simon Tam and Shepherd Book. River also qualifies. She may be a horrifically brutal and efficient killing machine, but she doesn't want to be one, and is terrified of her abilities.
Spock on Star Trek. The Federation as such would also fall under this category.
Lee "Apollo" Adama on Battlestar Galactica. He's a crack pilot and tactician, second only to Starbuck, but finds it difficult to carry out out orders he has ethical problems with, and actively questions the decisions behind them on occasion.
Sheridan's mantra is "We will not start the fight, but we will finish it!" He lives up to it, as in almost all battles he commands, he allows the enemy to make a first shot.
In a novel Sheridan's predecessor Sinclair said during his introductory speech to the recruits of the newly found organisation of Rangers, that those who'd joined to have revenge on Shadows are not welcomed there, as the ultimate goal of the organisation is to save lives, all lives, including those of Shadows, if it's possible.
Highlander: The Series: Methos is the oldest living immortal at 5,000+ years. In the present, he prefers to stay out of the Game and usually avoids fights. However, every now and then some other immortal will try to force the issue, only to learn the hard way that there's a damn good reason he's survived as long as he has.
"Just because someone doesn't like to fight, doesn't mean they can't."
Piffany in Nodwick is perhaps nauseatinglynice, but can and will fight alongside her teammates when faced with the forces of naughtiness.
Our Little Adventure: Julie, the heroic protagonist hates fighting, especially humans and other humanoid races. She got deeply annoyed when her friends celebrated her popping her 'kill cherry' in this comic page.
"I'm no hero. Never was, never will be. Just an old killer, hired to do some wetwork."
Flonne the Love Freak in Disgaea not only annoys her demonic friends and teammates with her endless prattle about "Love" and "Peace", but is quite a powerful magician and caster and helps out in fights.
Iji starts out as one. She may get less reluctant later in the game, depending on the player's actions. Ansaksie is definitely one, but Vateilika and Yukabacera may also count.
Shirou in Fate/stay night starts with the goal of only stopping Master's who are being actively disruptive and is absurdly forgiving of the likes of Shinji or Ilya. He tries diplomacy whenever practical, even with Kotomine and Caster. Unfortunately, when these efforts invariably fail, his only means of fighting back or even self defense involves putting swords in people's faces. Really, that's a very effective method of self-defense.
Zone of the Enders: Leo Stenbuck is intially extremely reluctant to fight even when his entire colony is being destroyed around him. Only near the end, when his 'girlfriend' has been shot, does he willingly continue fighting, even though a way out was staring him right in the face.
Tales of Symphonia: Dawn of the New World: Emil is not only a reluctant warrior, but incompetent at that. He can only do any good in a fight when 'possessed' by Ratatosk, who obligingly does so before every battle (except at certain parts of the game).
Luke in Tales of the Abyss becomes one of these as one of the earliest stages of his rather extensive Character Development. At first he's downright traumatised by the experience of killing a fellow human being in self-defense. It's only when his hesitation puts himself and his companions in danger that he begins to accept that it is kill or be killed on the battlefield. And while he does eventually learn to let go of his reluctance and face his enemies without hesitation or regret, it's stated that even then he's still toubled enough by it that he's left lying awake shaking at night.
Mass Effect: Through certain dialogue choices, Commander Shepard can come off as this.
In the third game, Shepard can admit to feeling like their entire life has been enslaved by warfare and expresses the hope that after the Reapers are defeated, they can finally be free.
In Red Dead Redemption, a game set during the dying days of the Wild West, John Marston becomes this. John was trying to give up his old life as a gang member in the Wild West by living on a ranch with his wife and son earning a humble living as a farmer. This plan is ruined when government agents kidnap his family and tell him that he will never see them again if he doesn't kill the members of his old gang. John complies and takes up his gun again for the sake of his family.
In Soul Calibur V, Pyrrha Alexandra is this to the extent that her default stance is leaning back with her shield pressed up against her. She's quite the fighter if pushed, but she really doesn't want to.
Hawke in Dragon Age II with a sarcastic personality definitely can come off as this, just wanting to live a quiet life, provide for their family and not deal with all the insane politics in Kirkwall.
Amagiri Kyuuju in Hakuōki always attempts to talk his would-be opponents into walking away, and enters combat only with great reluctance. Then he curbstomps you.
Post-World War 2 Germany as a whole. After the shock of what Just Following Orders can lead to, the new German constitution gave every German citizen the right to refuse military service, to prevent instrumentalization of German people by the occupying powers. In the face of the Cold War, the creation of a new german army was highly controversial and required a legal loophole to reintroduce conscription, despite violating the consitution. It wasn't until the Yugoslaw Wars in the 90s, when genocide was happening right next to EU borders, that German aircraft engaged in combat action, and even that was extremely controversial. Caught in the frenzy of late 2001, Germany supported the invasion of Afghanistan with equipment and technical specialists and later took control of the mostly pacified Northeast in a mission to "provide security for the population and projects for the development of local security forces". A landmark was reached in 2009, when the Minister of Defense first admited that German troops in Afghanistan were dealing with "conditions similar to war", which was criticized by many other politicians, who went to great lengths to reassure that german troops were not involved in any war. At the same time, Germany has the worlds 7th largest defense budget and is the worlds 3rd largest weapons exporter after the US and Russia. While Germany hates to use military force, it's really good atmaking weaponsnote Good at making weapons? How about good at making anything.
The Karate Kid example above is very much Truth in Television at least among traditional, "serious" practitioners or teachers of Eastern martial arts. Those are primarily present in the respective countries of origin, because in the West, these martial arts are most often treated as sports or mere self-defense mechanisms, focusing only on the combat. However, Eastern martial arts usually come with an entire philosophy attached and many, if not most, of those who practice their respective art traditionally will adhere to core points of these philosophies. Especially in Shotokan karate, the core philosophy is that actual combat should always be the very last resort and deescalation through "diplomacy", or, worst case, non-violent intimidation and other non-violent means should always be tried first. Only when there is no way to avoid a fight at all should the "martial" part come into play. This is part of the self-view of the karate practitioner, since the underlying philosophy teaches virtues such as humility, calmness, respect etc. Many other traditional martial arts are similar, but this component is mostly lacking in their Westernized forms or in MMA.