Morality Trope, potentially overlapping with Race Tropes. A character who has experienced some form of oppression or injustice in the past or has a background that makes it likely they or their family have suffered such a fate will not stand idly by when others are subjected to the same form of oppression or injustice, often making witnessing such mistreatment hit close to home and a special form of Berserk Button for this character and motivating them to become the Bully Hunter or liberate the slaves, or creating/joining a La Résistance group.
Sometimes it is merely implied by the character's (or actor's) race that they may have had personal experience with or knowledge of that kind of oppression, even if such experiences are not actually portrayed in the story or, sometimes, even part of the setting, potentially also making this a case of Unfortunate Implications (though usually in a at least somewhat positive fashion, as a character who is this trope is heroic rather than monstrous or villainous) or Values Dissonance.
A heroic character who fights any form of injustice or oppression isn't necessarily this — in order to be considered this trope, it must be specifically the same form of injustice that you suffered that you fight, or at least initially so, as such an occasion could also serve as the call that starts the character on a true hero's journey. May lead to a HeelFace Turn if an initially antagonistic character decides to take the moral high road, and may also become a case of Evil vs. Evil if a villainous character does fight injustice but resorts to less than heroic means to do so. If an antagonist does not reform, at least expect a Pet the Dog moment.
A character being this trope differs from being a Defector from Decadence or The Atoner in that the character did not use to perpetrate, espouse or tolerate the kinds of injustice they are now fighting, but used to actually suffer them (e.g. a slaveholder who starts fighting slavery is not this trope, and neither would be a character who neither was a slave themselves nor had members of their family enslaved, but a former slave or one of their descendants would be). This also makes this trope a (usually heroic) inversion of the Freudian Excuse in that the abuse you suffer does not lead to you inflicting abuse on others but to you protecting others from suffering the same fate.
- Fate Testarossa from Lyrical Nanoha is a failed mad science experiment who survived rather horrific parental abuse as a child. Upon growing up, she makes it her life's mission to save abused and ostracized children, especially those whom most people wouldn't even consider human.
- One Piece: Having suffered from starvation in the past, Sanji will help anyone close to him who's hungry, even potential enemies.
- Magneto is one of the most famous characters motivated by this mindset. As a Romani/Jew/other ethnic minority during World War II, he and his family suffered horribly at the hands of the Nazis, and he learned firsthand the terrible results of bigotry and hatred. To that end, he opposes that same treatment towards mutants. However, Magneto's methods are very much a case of Depending on the Writer, as sometimes he is 100% correct or even heroic while at other times he is treated as a Well-Intentioned Extremist who Became Their Own Antithesis. It depends on whatever the current status-quo is, really.
- This is almost a hat for X-23:
- Being an Opposite-Sex Clone, Laura is extremely sensitive to genetic experimentation and exploitation. It lead to her siding with the Sisters against Alchemax in All-New Wolverine, and the central plot of the Tamaki series involved her hunting down and shutting down further attempts to experiment on her genetics. She has outright stated that she refuses to let anyone else suffer as she did, and intends to make good on that promise.
- Additionally, Laura spent some time as a Street Walker under a particularly sadistic and cruel pimp. As a result, she's evolved into something of a Wife-Basher Basher who goes out of her way to bust up any human and sex traffickers she comes across. On several occasions she has outright killed people she caught brutalizing prostitutes (and in one case killed a man who murdered a girl she thought was a prostitute).
- In Dragon Age: Blue Wraith, the title character is a former slave who (since being freed from his master's control in Dragon Age II) has taken up the cause of Slave Liberation in the heart of the Tevinter Imperium, particularly targeting magisters with designs of turning their slaves into Living Weapons — like his former owner did to him.
- Invoked and inverted by Erik Killmonger in Black Panther (2018), who has personally experienced racism and discrimination while growing up in the USA and now intends to save other Black people around the world from suffering similar fates by arming them with advanced vibranium weapons, at the very least ignoring and probably being fully aware that the people he arms will merely become the new oppressors in turn.
- In the zombie comedy Deadheads, Thomas Jeremiah, who is African-American, hunts the intelligent and quite harmless zombie protagonist for a shady corporation. When it becomes clear that the corporation intends to enslave the zombies, this prompts Jeremiah's HeelFace Turn, and he helps the zombies escape and reach the girl who happens to have become engaged to one of the zombies before he was turned.
- In District 9, Wikus initially does not seem to mind harassing and even killing the aliens while he is still human. It is only later, when he hasn't only started turning into an alien himself, but has also been treated as less than human and even been experimented upon by humans that he starts fighting alongside the aliens, though it is not made clear whether he is truly doing this because he, having suffered the same treatment, now sees it as wrong and fights it for that reason, or because he still believes he needs to protect the aliens so they can turn him human again.
- In Gattaca, Vincent allows the wind to carry away a genetic sample given to him by Irene when she is clearly afraid he will reject her because of her imperfect genes. Actually having used bought genetic samples to assume another man's identity after having been discriminated against because of his own imperfect genes all his life, Vincent knows exactly how Irene feels.
- In Hellboy II: The Golden Army, pyrokinetic Liz Sherman bursts into flame when a crowd throws a rock at Hellboy, turning the whole situation into a Face-Heel Temptation, but manages to restrain herself and merely launch into a "Reason You Suck" Speech. A flashback in Hellboy (2004) showed that Elizabeth had had rocks thrown at herself, too, when she was still a little girl and her powers were manifesting uncontrollably, which then resulted in an explosion that killed several bullying kids.
- In Iron Sky, James, who is African-American, is pretty much the only decent person in the entire film (apart from the people of Finland). While this isn't difficult when the antagonists are actual Nazis From Space, James also both fights the Nazis with violence as well as by working to deprogram those who just don't know things could be different. Additionally, the fact that the US President deliberately sent James to the moon in a publicity stunt to get the Black vote shows that discrimination against African-Americans is a thing in the film's setting that requires patching up, or at least papering over, in the President's eyes.
- The African mercenary Albert Laurent decides to help the main characters in The Island. Their tattooed numbers, which identify them as clones - their lives to be thrown away for the benefit of their purchasers - remind him of the reason he was branded himself as a child, making him switch sides.
- In the 1986 film version of Little Shop of Horrors, Audrey II can only tempt everybody's doormat Seymour into committing murder when they watch Audrey being treated the same way.
- In Frank Herbert's Dune series, the Bene Gesserit struggle to improve humanity because they have inherited all the atrocities humanity has both suffered and inflicted through their Genetic Memory (though it would be argued by the Bene Gesserit themselves that this is more of a case of the Bene Gesserit being the atoners rather than opposing what their genetic ancestors suffered, since they only inherit the memories of survivors - which usually means the memories of those who perpetrate atrocities rather than suffer them).
- Several cases in Sir Terry Pratchett's Discworld:
- In Small Gods, Brutha is used (and abused) as a useful pawn (or sacrifice) by the authorities of the Church of Om, the god Om himself, and even by those opposing the church. Later, once Om has regained his power and instated Brutha as the new head of the church, Brutha works to reform the church as well as his own god to make sure that people are never treated as mere pieces on a chessboard by the church or his god ever again. This has backfired a bit by the time of Carpe Jugulum, but still.
- In Unseen Academicals, Pepe stands up to the bully Andy when no-one else does, both by providing the protagonists with protection against Andy's favoured Groin Attack and by actually cutting Andy with a knife, a treatment Andy is very keen on inflicting on others, and in his "The Reason You Suck" Speech Pepe states that he is very familiar with bullies, implicitly from having been bullied himself, potentially about his ambiguous species and sexuality, and will not allow bullies to get away with it any more.
- In the Harry Potter series, Harry was raised by his abusive aunt and uncle. This contributes to his empathy for others who've been abused, like Dobby the House Elf.
- Katniss Everdeen of The Hunger Games trilogy, having survived the eponymous Gladiator Games twice (in consecutive years to boot), is not at all amused with the notion of the game being set up one more time involving the Capitol children, to the point of personally killing Alma Coin for (among other things) coming up with this proposal.
- Night World: Rashel Jordan eventually fights to protect innocent people, especially kids, from being harmed by dangerous Night People; as a little girl her family was killed by a vampire and she only narrowly escaped herself.
- In A Song of Ice and Fire, Daenerys Targaryen opposes slavery, to the point of conquering all of Slaver's Bay to free their slaves, because she herself knows what it's like to be treated like property; her brother Viserys gave her as a wife to Drogo when she was only thirteen in exchange for an army, not caring in the slightest that she didn't want to marry him or how Drogo treated her as long as got what he wanted.
- (Unsurprisingly) several cases in Star Trek:
- In the second season Star Trek: The Next Generation episode "The Measure of a Man", the android Data's rights are contested, as a scientist argues he should be treated as a machine, rather than a person, and this fact is even demonstrated by Data being taken apart and switched off without his consent. In the season 6 episode "The Quality of Life", Data then goes to extreme lengths to protect an emerging machine life-form from being treated in the same manner before they can fully achieve sentience, even going so far as to risk the life of his own best friend, Geordi La Forge.
- In the fifth season Star Trek: Deep Space Nine episode "The Begotten", the former shapeshifter Odo tries to raise an infant shapeshifter. When Odo himself was an infant, he was treated as a mere lab specimen and even subjected to painful experiments before he could convince the scientists he was self-aware, and now he works hard to protect the infant shapeshifter from suffering the same fate, refusing to allow even the man whose experiments helped Odo gain control over his own shapeshifting abilities in the first place to help. Instead, Odo chooses to raise the infant shapeshifter in a very gentle, nurturing manner. Eventually, however, the scientist who raised Odo demonstrates that raising an infant may also require a bit of Tough Love on occasion when Odo's progress hits a wall.
- Volk from Dragalia Lost exploits (and misappropriates) this trope: The details available on his background show that he came from a life of absolute poverty, struggling to get by and having nothing whatsoever to his name. Blaming others for his deprived youth, he now fights anyone with privilege or in a position of power no matter whether they are responsible for anyone's suffering or not - he is introduced murdering a mayor who has used his influence to help his townspeople prosper.
- In Journey, the various cloth creatures you encounter used to be used to power the machinery and engines of war of the Ancients. When you free some of these creatures from the machinery they are trapped in, they will insist on leading you to other entrapped cloth creatures so you can free them as well.
- Several cases in Knights of the Old Republic:
- Juhani wanted to become a Jedi knight to fight against awful conditions like those she and her family used to live in when they were fugitives.
- The villainous Yuthura Ban wants to complete her Sith training to gain the power to free slaves explicitly because she used to be a slave herself, which would also make this a case of Evil vs. Evil - by the time you meet her she has certainly become a Well-Intentioned Extremist at best, and is close to even Jumping Off the Slippery Slope and abandoning her heroic cause entirely.
- Several instances in the Mass Effect universe:
- In Mass Effect, the biotic Jack was both a captive and a test subject of Cerberus when she was a child. If she survives the Suicide Mission in Mass Effect 2, Jack later becomes the Mama Bear (if Tough Love-practising) teacher of a group of young biotics in Mass Effect 3, when Cerberus comes back and attempts to abduct them in order to turn them into biotic assassins.
- Pretty much all the civilisations already wiped out by the Reapers in previous cycles who have been working on the Crucible, a device that is supposed to end the Reaper threat once and for all, count, because they clearly want to make sure the same thing does not happen to other civilisations even if it is too late for themselves. Also counts as Flinging a Light into the Future.
- Street Fighter: The reason Chun-li becomes an Interpol agent is to stop the evil organization Shadaloo from ruining more people's lives, after they played a part on her Dark and Troubled Past (i.e having her father killed).
- In Ikemen Sengoku, Hideyoshi is especially passionate about Nobunaga's plans to create a more equal world and always does his best to stand up for the lowest members of society because he himself grew up in poverty and specifically, as a member of the Sanka gypsies, a maligned ethnicity and was only saved from that status due to Nobunaga's charity.
- Ensemble Stars!: In a downplayed example, Adonis grew up weak and sickly which led to him being taken advantage of by some stronger people. Now that he's grown up into a fit and strong man, he often repeats a declaration to protect the small and weak, because he knows what it's like to be powerless.
- Defied by Archibald Snatcher in The Boxtrolls, who, as a "Red-Hat," is of lower social status than the "White-Hats," but is quite willing to step on those who are even lower on the rungs of the social ladder than himself, i.e. the eponymous vilified boxtrolls. Played straight and even lampshaded by the Red-Hats Mr. Trout and Mr. Pickles, who have a Heel Realization and, even when faced with failing to obtain a better social status by doing so, decide to aid the oppressed boxtrolls and their human allies Winifred and Eggs.
- Trevor Belmont, the last remaining member of the Belmont Family in Castlevania. Following centuries of hunting monsters to protect the people of Walachia the Belmonts were falsely accused of practicing black magic by corrupt members of the clergy, leading to his ancestral home being burned down and his parents murdered when Trevor was eight years old. Whilst this has left him cynical and jaded towards most of mankind, Trevor also possess a deep empathy towards those who are unfairly persecuted by the corrupt. Protecting a nomadic group called the Speakers from being scapegoated by a corrupt bishop marks his transition from simply drifting through to actually taking a stand in general.
- In Corpse Bride, Emily had her happiness stolen from her when she was murdered for her dowry by the man she had eloped with. At the end, she protects Victoria from a similar fate even at the cost of her own happiness, and especially because it would now have been Emily who inflicted such a fate on another bride, because she knows exactly how painful it is.
- Zigzagged two ways from Sunday in Transformers: Prime: Megatron started out as a nameless transformer slaving away in the mines underneath Bad Bosses, and eventually found his way to the Gladiatorial pits, where he earned his freedom through his victories, taking the name 'Megatronus' after the original Tragic Villain of the mythos in the process, hoping to strike fear into his gladitorial opponents. After earning his freedom, Megatronus gathered a following of disenfranchised transformers and campaigned for a reformation of the political system of their home planet, Cybertron, to make it more egalitarian than it was at the time... but when he was finally granted an audience with the Not-So-Omniscient Council of Bickering that ran the planet, he saw the flaws inherent in the political process and demanded that he be named Prime - supreme ruler. When this was refused and one of his long-time friends was given the opportunity instead, his gathering of loyal followers began a Civil War against the rulers of the planet to make — the now-renamed — Megatron ruler, a Civil War that would, after milennia of conflict, eventually render the planet uninhabitable and every single remaining transformer The Remnant, and saw his followers rename themselves the 'Decepticons' as their goals eventually became little more than totalitarian control of everything. The final zig of this zagging comes at the end of the series, where Megatron has been possessed by Unicron, and is Forced to Watch as Unicron uses his body for the purpose of finally killing off the dormant Primus at the center of the recently-restored Cybertron. Whenever Megatron tries to resist, Unicron enacts Cold-Blooded Torture upon his soul - and this leads to Megatron having a Heel Realization. When the possession is lifted, Megatron disbands the Decepticons and leaves for voluntary exile, realizing that his attempts at becoming this trope have utterly failed, and that no matter what he does now, his millennia of warfare mean he will always be remembered as an Evil Overlord.
- Frederick Douglass (1818-1895), who had himself escaped from slavery, fought for the abolition of slavery as well as against other forms of political discrimination.
- Elie Wiesel, a surivor of The Holocaust and the author of Night, spent his life after the Holocaust as an advocate against genocide.
- Emily Lindin, a feminist activist who founded anti-sexual bullying website The UnSlut Project did so due to slut-shaming she experienced in middle and high school.