In Cars, Doc Hudson used to be a race car until 1954 when he crashed violently during a race. After getting repaired, he was replaced with the next rookie in line and never raced again.
Also Cruz Ramirez from Cars 3. She wanted desperately to be a racer just like Lightning McQueen and took up classes with much bigger cars, but by the time of her first race when the other cars were starting, she simply left the race behind and lost her only chance.
Kovu from The Lion King II: Simba's Pride was raised by his vengeful mother to become Scar's successor and trained to be a hateful war machine so he can kill Simba.
Marlin in Finding Nemo: his wife Coral and all of his eggs, except for Nemo, were eaten by a barracuda, which is why he's so overprotective of him.
Megara in Hercules: she sold her soul to Hades in order to save her boyfriend, and he dumped her shortly after that. Also, it's hinted that she probably had more problems to face in life besides that.
Lampshaded in Wreck-It Ralph: Sergeant Calhoun "Was programmed with the most tragic back-story ever." Her lover was killed in front of her by Cy-Bugs on their wedding day, and she blames herself because she forgot to do a perimeter check for enemies. It's part of why she's usually so on edge about the Cy-Bugs and aggressive.
It turns out that Po of all people has one, though he doesn't learn about it in full until just before the climax. It involves the attempted massacre of his entire species by Lord Shen and his birth mother sacrificing herself to save him.
Tigress. She was left by her parents in an orphanage, called a monster by adult and child alike and was not shown any signs of parental love by her foster father, Shifu.
In The Snow Queen (2012), The Snow Queen's backstory shows her as a girl whose natural sorcerous powers were so strong that she was rejected and mocked by her people.
Queen Elsa goes through her greatest failureas a child. She strikes her sister Anna in the head with her icy powers, causing her to fall unconscious. The trolls heal Anna and remove her memory of the event and her sister's magic, but she still comes out with a white stripe in her hair, thanks to the ice magic. In case you thought that seeing your sister's white stripe of hair and being reminded of your largest mistake wasn't bad enough, the trolls also warn her about the potential of mobs attacking her if she doesn't learn control, which also makes her fear for her life. Then her father tries to protect her from such a fate by keeping the magic a secret (even from Anna) and isolating her, locking her up in the castle. This essentially drives the entire plot and is the reason why Elsa is so detached from her sister and avoidant in general.
Anna is a naturally extroverted person who is forced to be isolated from others for the majority of her childhood. To make matters worse, she doesn't know why it happened, and from her perspective, her older sister suddenly cut off their friendship and then ignored her for no apparent reason. Her parents are implied to focus on her sister, and then they die when she is fifteen, and again she has no emotional support. Her sister still shows no interest in talking to her or even attending their parents' funeral.note Unbeknownst to Anna, this is because of Elsa's Power Incontinence, but Elsa keeps this a secret, so Anna doesn't know why her sister seems so uninterested in her. It's obviously left some scars on her, and is a big reason why she agrees to a quick engagement, because she's starved for affection and isn't familiar with what a healthy loving relationship looks like.
In Trolls, the reason why Branch lost his colors, refuses to sing, is a bit of a Grumpy Bear, and is massively (but rightfully) paranoid of the Bergens attacking is because when he was a kid, his singing attracted a Bergen, and Branch's grandmother got eaten when she tried to save him.
The Little Mermaid III: Ariel's Beginning reveals how King Triton's beloved wife Queen Athena was accidentally struck to her death by the ship's hull, which led to him banning music from Atlantica and the merpeople from going up to the surface in grief. After the incident, King Triton became over-protective of his daughters - especially Ariel - and displays his racism towards humans for his wife's death.
In Quest for Camelot, Garrett reveals to Kayley in the past, he was accidentally blinded by one of the horses that he was rescuing from the stable fire. Thankfully, Sir Lionel still believed in him and taught him to adapt. Unfortunately, his situation worsened when he heard of Sir Lionel's death, prompting Garrett to go into self-exile into the Forbidden Forest.
The eponymous Max Payne has one, his family was killed in a mysterious robbery. Made extra saccharine thanks to the Flash Backs being in a warm ember tone compared to the rest of the film's drab winter blues and grays.
To be even more specific, in the game the movie is based upon, his family got killed by V-head junkies as part of an attempt to silence Max's wife for knowing too much about Project Valhalla. Tragically, Max's wife didn't have a clue what the memo meant and wanted to talk to Max about it, but he didn't listen to her because he had to go to work for the day.
The emotional turmoil brought on by the childhood abuse of Tim Robbins' character is the main crux of Mystic River.
Gabriel in Van Helsing also has Wolverine Amnesia, it's implied by Dracula they both share "a history" together, and even hints at Gabriel being an immortal "tripped" angel or the like, but nothing concrete ever comes of it. Sequel Hook?
Johnny Guitar's main characters Vienna and Johnny "Guitar" Logan have dark pasts dealing with their former lives as a prostitue and a ruthless gunslinger.
O-Ren Ishii from Kill Bill lost both of her parents to vicious Yakuza gangsters at the age of seven and then getting her revenge just four years later.
The main character of Hoosiers, Norman Dale, moves to the small town of Hickory, Indiana to take one last shot at redemption as a basketball coach after ruining his coaching career many years earlier when he lost his temper and punched one of his own players.
Subverted in The Dark Knight, where the Joker likes telling stories about his Dark and Troubled Past to explain his scars...but every story is different. This is a tribute to Alan Moore's The Killing Joke, wherein The Joker has the following line; "Sometimes I remember it one way, sometimes another...if I'm going to have a past, I prefer it to be multiple choice!"
The first five minutes of The Descent kill off the main character's husband and young daughter, leaving her traumatized and sometimes hallucinating. A big part of what fuels her trip into Ax-Crazy, particularly if the monsters don't really exist.
The Terminal: Gupta explains to Victor why he is so obsessed with keeping his janitor job: he was a poor tobacco dealer in India who was shaken down by a corrupt police officer. Eventually, Gupta stabbed the bastard in the chest after several days of extortion, and fled India and his family to not be charged with assault. By working as a janitor, he can remain off of anybody's radar. Dixon threatens to have Gupta deported if Viktor doesn't leave.
The first five minutes of the Prom Night (2008) remake feature the protagonist coming home to find her father and brother dead, and watch her mother get killed, all because the killer was looking for her. For her character, this doesn't really come into play much for the rest of the movie, even when the killer comes back.
Princess Leia from Star Wars. She remembers her (presumably adoptive) mother always being unhappy when she was young, saw her homeworld destroyed as a You Said You Would Let Them Go, has (in the Legends continuity) seen one son KIA and the other do a FaceHeel Turn — his twin sister was forced to kill him; the Disney continuity also has her son do a FaceHeel Turn, which ends with him killing his father and taking control of the First Order.
Given that the main characters in The Way Back are seven gulag escapees and an orphan, this is something of a given. None of the men will tell each other their stories, but they all tell the girl, who, in turn, passes them on to the others. When she asks why they don't talk to one another, she's told that, in the gulag, the less you say, the better off you are.
Jack/Kyra during the Time Skip between Pitch Black and The Chronicles of Riddick. She ran away to search for Riddick and signed up with a bunch of mercs, only to be enslaved, with a heavy implication as to what kind. Made worse in that she was only twelve at the time! Riddick is understandably pissed to learn this, as well as furious at her for ignoring his single instruction when they parted ways;
Riddick: I told you to stay on New Mecca. Did you not listen!
Something that happened "in Chicago" to Lucien Carr in Kill Your Darlings is repeatedly alluded to, much to his displeasure.
Both Eddie and Sarah in The Hustler have this; she even lampshades it when they first meet.
Sarah: Eddie, look, I've got troubles... and I think maybe you've got troubles. Maybe it'd be better if we just leave each other alone.
In Sidney Lumet's The Pawnbroker (1964), the main character is traumatized by what happened to him and his family in a WWII Nazi concentration camp. He hasn't been able to work through his issues, which causes those unpleasant memories to regularly flood his mind.
In The Hunger Games Katniss' father died when she was 11 in an accident that she suspects the government to have orchestrated. Without the father's income, the family starved and Katniss nearly died, which is why she is so survival-focused.
The Wolfman (2010): You've had quite a nice little messed up childhood, haven't you, Lawrence? What with witnessing your mother's death and all, and being sent to a mad-house where you underwent all sorts of nasty treatments and then shipped off to live with a distant relative in America.
Magneto. "Holocaust survivor" is about as dark and troubled as it gets. He eventually settles down with a wife and daughter, only for them to die as well. It's no surprise Erik isn't exactly a ray of sunshine these days.
Wolverine's past history of fighting in the American Civil War, World War I, World War II, the Vietnam War, and his past work with Team X. How much of it still happened after the Cosmic Retcon is unclear, but we do get to see him escape from the Weapon X project in a flurry of adamantium and rage, so it's clear that the Broad Strokes of most versions of his origin still stand, and it ain't pretty.
In The Wolverine, Yukios first premonition was her parent's death, and after she was forced to watch it come true, she became a street urchin scavenging for food until Ichiro Yashida found her and adopted her under his wing.
Jack, of Jack Brooks: Monster Slayer, had his family killed in front of him by a monster when he was a child. He ran, the only thing he could do, but it's eaten at him ever since, fueling his Unstoppable Rage and inspiring him to step up to become a hero.
In The Lazarus Effect Zoe survived a fire that killed many people in her apartment complex. She's had recurring nightmares of it for years. Turns out she set it.
In Kingsman: The Secret Service, Eggsy's father died in action, and his mother remarried a jerkassdomestic abuser who liked to beat the crap out of Eggsy and his mom. At some point, Eggsy resorted to drugs and petty crimes. By extension his half-sister Daisy has this too, despite not even being old enough to speak yet: her own father is the domestic abuser and her own mother nearly killed her during the Valentine's Day Massacre.
Assassin's Creed (2016): Callum Lynch's father killed his mother according to the Creed to preserve the secret of the Eden Apple of Granada as modern-day Templars led by Alan Rikkin were coming for them. Little Cal didn't know any of that so he grew up an orphan hating his father and drifted in and out of correctional facilities.
Chisolm was a USCT in the Civil War and became a bounty hunter after witnessing his mother and sisters being raped and killed by Borge's hired men.
Jack Horne had a wife and children but lost them in an unspecified event. It's hinted that their deaths were related to him hunting and killing Indians for a government bounty.
Vasquez is wanted for a Texan ranger but no details are given except Vasquez suggesting he had it coming.
Goodnight is a former Confederate sharpshooter suffering from PTSD and survivor's guilt.
Billy is a Korean immigrant who was an indentured servant who killed his masters and ran away.
In Manchester by the Sea, the protagonist Lee was once a cheerful and outgoing, if somewhat irresponsible, father and husband. Then, while he was high and drunk one night, he accidentally started a fire that burned down his house and killed all of his children. After being questioned at the police station, he attempted suicide, forcing him to leave town and become a recluse. As a result, he's been reduced to a shell of a man and a jerkass woobie by the start of the film, unable to forgive himself.
In Death Grip, Kenny and Mark lost their mother in a house fire. They both have unresolved guilt over it. The fire was started when Kenny was playing flammable material outside and the mother died because Mark locked the door behind him due to his Ambiguous Disorder, trapping his mother in the burning house.
Fast Color: Ruth ran away from home due to her uncontrolled abilities, was hooked on drugs and then got pregnant (without knowing who the father is). Then she came home with her daughter Lila, but left when her powers endangered the baby, becoming a wanderer for years before finally returning.
My Days Of Mercy: Lucy reveals hers to Mercy. Her mother was murdered, and her father is now on death row for doing it (but she doesn't believe he's guilty). His date for execution is only months away.