Origin Story/Examples

Anime and Manga

 * Naruto:
 * Orochimaru: As result of his parent's death during the war, Orochimaru became disillusioned with the reality where all living being would die someday, and sought to become the strongest shinobi in the world and an immortal via combining kinjutsu and various experimentations.
 * Mizuki: Due to his personal obsession to be the strongest shinobi that escalated to unhealthy level, Mizuki became indifferent with by things like morals or teamwork (traits which made Orochimaru became interested by him that he gave him Curse Mark that would activated through certain drug combination as seen in anime) and ultimately became a villain and one of Naruto's most dangerous advesary during his youth.
 * Dragon Balls series:
 * King Piccolo: The demonic Piccolo was originally the evil part within a powerful Namekian. When the said Namekian expelled all evil within him, his expelled evil manifests into Piccolo whom born with flesh and blood like regular Namekian, but only carry malevolence within his creator. In spite of his, his final spawn, Piccolo. Jr., whom Piccolo created to avenge his death and initially believed as evil as his parent, revealed to be born as regular Namekian who lacked his predecessor's malevolence in spite of possessing powers that as immense as the former. The lack of his parent's malevolence of course, what contribute to Piccolo Jr.'s choice to become a good person.
 * Scar (Fullmetal Alchemist): Sought revenge on every State Alchemist for the Ishvalan massacre many of them have comitted.

Comic Books

 * Man-Bat: Dr. Langstrom's attempt to cure his deafness with help of serum based on bats' DNA and to help those whom are deaf and blind and test the serum on himself, only to ended up turned into humanoid bat-like monster. This prompt Batman to cured him to normal.
 * The Lizard: Similar with Dr. Langstrom's case, Dr. Connors creates a serum based on lizards' DNA to create regenerative serum that would beneficially help those whom became disable or severe injuries where he test the serum on himself that not only regrows his right arm, but ended up transformed into a humanoid lizard where Peter Parker had to create a cure to restore him.
 * Magneto: Having survived Nazi Holocaust during events of World War 2 where his powers manifests for the first time and sees mutants whom mistreated due to jealousy, hatred, or prejudice in reminiscent way Nazis mistreated many innocents includes himself, he sought to ensure that mutants would live in peace in the world, but in more extreme way than his friend Xavier's methods as he also believed that mutantkinds are better than humanity.
 * Scorpion: Mac Gargan, the nasty private investigator whom hired by J. Jonah Jameson to stalk on Peter Parker to find out how he can easily get his alter ego Spider-Man's photos, conspired with his client to defeat the web-slinger with Dr. Stillwell's help whom enhanced his DNA with that of scorpion that grant him superhuman capabilities and a scorpion suit and become the notorious supervillain called Scorpion upon the revelation of his genetic enhancement would render him insane as Dr. Stillwell's feared.
 * Apocalypse: When EN Sabah Nur was born, he was abandoned of having grey skin, blue lips, and unusual facial markings. He would eventually rise to become a strong warrior and soon, a powerful mutant by mastering his powers and acquiring alien technology. He would be worshipped as a god by many and years later, he would awaken from dormancy into the modern world and pose the biggest threat to the X-Men as he would seek to destroy the current world and build a new one in his image referred to simply as the Age of Apocalypse.
 * Jason Todd (nicknamed Red Hood): Disillusioned by Batman's code not to kill his enemies, which worsened with his near-death experience by Joker whom intended to killed him, Jason Todd, upon survived his ordeal (resurrected in some versions soon after killed outright), decided to become a villainous vigilante called Red Hood.
 * Darth Wredd: Darth Wredd himself was a normal human boy when his hometown was destroyed by a band of barbarians and was eventually inducted into the One Sith after his homeworld was invaded by the Galactic Empire lead by Darth Krayt. He was instructed in the ways of the dark side of the force, but soon found out that his entire homeworld was destroyed by the One Sith and defected to seek revenge against them and restore the Sith Order under the ancient Rule of Two.

Animated

 * Aggie Prenderghast (ParaNorman): Sought revenge on the townspeople as well as Judge Hopkins for their discrimination against her.
 * Lord Shen: He became disturbingly obsessed with fireworks as he saw they could also be used in warfare. His concerned parents consulted the Soothsayer who foretells Shen's destined downfall at the hands of "a warrior of black and white." Shen overhears this prophecy and decides to avert it by massacring a nearby village of  innocent pandas. Shen returns to his parents with sadistic joy, but his parents, horrified that their son would do such a wicked deed, banished him from the city as punishment. Shen, believing his parents hated and wronged him, vows revenge that he will return to Gongmen one day.
 * Syndrome: Buddy Pine, also known as IncrediBoy, wanted to become Mr. Incredible's sidekick and joining him in his crime fighting, but he refused and eject him out of his IncrediCar. Later that night, IncrediBoy shows up and disturb the fight between Mr. Incredible and Bomb Voyage before Bomb Voyage put the bomb on his cape and Mr. Incredible saved him by pulling the bomb out from his cape. Because of getting sick of him, IncrediBoy got sent to his home by police and getting punished by his parents (even though it was never seen). Due to this, he finally grew hatred of Mr. Incredible and eventually become a supervillain.
 * Professor Screweyes: When he was a child, he was snoozing by a berry bush, and after a berry fell upon his eye, a crow pecked for the fruit, while at the same time, taking his eye. Ever since then, Screweyes decided that the world around him made no sense at all and therefore acts accordingly to life's senseless ways by using fear to get his way. Because of his incident, he had a fear of crows, and uses this as his act. This way, even while he fears the crows, they are still under his control.
 * Lots-O'-Huggin' Bear: Was the favorite toy to a little girl named Daisy. One day, Daisy's family took a little road trip, when as the family left, they accidentally left Lotso, Chuckles and Big Baby behind. Lotso and his allies walk for miles before finally reaching Daisy's house--only to discover Daisy has a new replacement Lotso. This tragic event causes Lotso to snap and turn evil and insane and he lies to the other toys that Daisy replaced them as well. Eventually, they came across Sunnyside Daycare and Lotso took control of the place and ran it like a prison for all the toys who resided there.
 * Francis E. Francis: Was a worker at Baby Corp known as the Super Colossal Big Fat Boss Baby eventually working himself up as its new CEO until he got kicked out for having lactose intolerance as he couldn't drink a secret formula that made babies act like adults, which resulted at him getting older, much to his dismay. After getting replaced and fired by the board of directors, Francis was sent to be adopted by the Francis family with an older brother named Eugene. Ever since then, Francis angrily vowed revenge on Baby Corp for this. Growing up to become a middle-aged businessman, Francis founded Puppy Co. to act as a rival to Baby Corp, becoming more popular and lovable to the public.
 * Robert Callaghan/Yokai: After a colleague lab test supervised by his colleague Alistair Krei goes haywire and results in Callaghan's daughter Abigail disappearing, Callaghan sets the entire building on fire--killing one of his students, Tadashi Hamada--and Callaghan escapes with Tadashi's brother Hiro's microbots. A year later, Callaghan has assumed the identity of supervillain known as Yokai and has sought revenge on Krei (whom he blames for the lab accident).
 * Phango: Was born with one blind eye and was abandoned by his clan as the runt of the litter. He was thrown in the magical water pond in the clan's lair. This only made the leopard stronger giving him an extra, almost mystical strong sense of smell. He become ruthless killer after killed his clan in revenge. He is obsessed with being whole.
 * Kai the Collector: Was a good friend and brother-in-arms to Master Oogway as they both were fearsome warriors that led their army against enemies. After an ambush that left Oogway injured, Kai carried his friend for days through harsh conditions looking for help until coming across to a secret panda village. Using the power of chi, the pandas healed Oogway and began teaching him the ways of chi. Kai, however, became obsessed with chi and sought to take and steal chi for himself. Oogway, who now became a better individual after having his life saved, saw how corrupted and dangerously obsessed his former friend had become, causing him to fight Kai in an attempt to stop him. They dueled each other until Oogway managed to defeat and banish Kai into the Spirit Realm. Despite being trapped in the Spirit Realm, Kai continued to take chi from deceased kung Fu masters for centuries until he had enough to return to the mortal realm and finish his mission; to destroy kung Fu and the world.
 * Ernesto de la Cruz: Was a childhood friend and music partner to Hector Rivera whom he convinced and traveled with throughout Mexico to work in the music industry. However, Hector grew homesick and decided to return home to his wife and child, secretly infuriating Ernesto. Pretending to support his friend, Ernesto secretly gave Hector a poisoned drink and watched as the poison killed him as they walked to the train station. Once Hector died, Ernesto stole his friend's songbook and guitar to become a musical legend and movie star until being crushed and killed by a giant bell in 1942.
 * The Toad: Out of all the pets in Buckingham Palace, The Toad was the favorite of Prince Charles. They would frolic, day after sunny day in royal abandon; sharing the bond between them. They were inseperable, until one day when Charles got a pet rat and The Toad was eventually flushed away into the sewers.

Live-Action

 * David Banner: Sought revenge on General Thunderbolt Ross for berating him for experimenting on himself and his son Bruce, and later tried to absorb his son's powers after gaining matter-absorbing powers.
 * In The Dark Knight, The Joker often changes his backstory, explaining how he got his trademark smile.
 * Toho's Godzilla films & MonsterVerse film series:
 * Godzilla: Godzilla's Toho incarnations were originally prehistoric intermediate reptilian lifeforms (clarified as Godzillasaurus in Heisei series and unspecified marine reptile in Godzilla: Resurgence) mutated by radioactive materials produced by either nuclear tests or nuclear waste dumped to his habitat which mutated him into nuclear-powered kaiju. The MonsterVerse incarnation however, gave him a more realistic origin as he was established as known still-living member of prehistoric reptile species that evolved by natural radiation on Earth during the prehistoric era.
 * Destoroyah: Destoroyah are malevolent monster that originally result of prehistoric crustaceans empowered by chemicals within Oxygen Destroyer used to kill first Godzilla. But in IDW comics, he was instead products of chemicals (with presumably coincidentally identical properties with Oxygen Destroyer) used by Devonians to bio-engineered same prehistoric crustaceans with similar results.
 * Keizer Ghidorah: Keizer Ghidorah is cryptic variant of Ghidorah with cryptic origin, as it's unclear whether Xiliens either engineered him or merely found him before out him under their control.

Literature

 * Lord Voldemort: Birthed from the impure, loveless union between Tom Riddle Sr. and Merope Gaunt, and later sought for immortality via Horcruxes when he discovered his magical inheritance, Lord Voldemort sought to rule the world which is pure from humanity and became the Dark Lord that is infamous to all to the day.
 * Sauron: Formerly a Maia of Aulë the Smith named Mairon, Sauron was seduced into servtitude for Morgoth, and is reduced into a fearsome new Dark Lord.

Live-Action TV

 * Azazel (Supernatural): One of the Princes of Hell created by Lucifer, Azazel schemed to create many Special Children who could potentially serve as his master's vessel and released many demons, chief among them Lilith so she could begin breaking the 66 Seals of Lucifer's Cage. He fed various babies, including an infant Sam Winchester, his blood to give them psychic abilities; he also murdered Sam's mother Mary, leading Mary's husband John and their two sons to become Hunters.
 * Ultraman Belial: Prior to his fall into an abomination everyone know and fear, Belial was originally one of Ultra Warriors. ut of envy towards his comrade Ken who became Space Garrison's Supreme Commander, decided to steal the Plasma Spark to become stronger. Banished for the said crime, the devastated and bitter Ultra then made a pact with Rayblood who then turned him into an Ultra Reionics.

Videogames

 * Alex Mercer: After the ill-attempt escape from Blackwatch soldier and is gunned to death not long after destroyed the vial of Blacklight virus that he took with him, Alex later rises as the new being which code named Zeus where the later plot twist revealed that Alex was already dead and his body actually possessed by the very virus that he released whom unknowingly took his identity.
 * Count Bleck (Super Paper Mario): Heartbroken at the disappearance of his beloved at the hands of his father, Lord Blumiere sought to destroy all the worlds for the world is meaningless for him without her.
 * Cole MacGrath: Cole was originally an ordinary man who worked as a courier and had his future self Kessler awakened his electrokinetic powers awakened with Ray Sphere explosion he instigated before faced several arranged tests as ordeal to see whether he will choose a good path or an evil path.
 * Shadow the Hedgehog: After being created by Professor Gerald, Eggman's grandfather, He and His granddaughter, Maria watched the Earth together, until the military intruded the A.R.K. and shut down the research. Maria's sacrifice was that she pleaded Shadow to bring hope to humanity as he promised.
 * Dr. Eggman: When he was a child he looked up to his grandfather because of the things he completed in his life. Eggman wanted to be a great scientist like Gerald.
 * Infinite: Infinite was once the captain of the Jackal Squad, a band of mercenary thieves raiding others for a profit. In time, he gained a public reputation as the "ultimate mercenary". One day, the ultimate mercenary led his squad on a raid of Eggman's base in the Arsenal Pyramid while the scientist was studying the Phantom Ruby in an attempt to steal his devices for a hefty bounty. Using the Phantom Ruby, Eggman created an army of Egg Pawn replicas to fend off the Jackal Squad. Slipping past the Egg Pawns, the ultimate mercenary ordered his squad to handle the robots while he moved in to kill Eggman with his sword. However, the ultimate mercenary accidentally struck the Phantom Ruby instead, causing it to show him an illusion of what he desired the most: a desolate, destroyed world. Using this to push the ultimate mercenary aside, Eggman, who also saw the vision, took a liking to him and offered to make him the leader of his Eggman Army so they could accomplish their goals together. Realizing he had grown bored of the world as it was, the ultimate mercenary took Eggman's offer in spite of his squad's protest. Some time later, the ultimate mercenary and the Jackal Squad got assigned by Eggman to guard his facility in Mystic Jungle. When Shadow the Hedgehog came to raid and destroy the facility however, the Jackal Squad got annihilated by the black hedgehog. Berated by Eggman for his squad's incompetence at protecting the facility, the ultimate mercenary caught up to Shadow and tried to ambush him as payback for what he did to his squad and to live up to his title. However, the ultimate mercenary was caught off-guard by Shadow's Chaos Control-abilities and ended up being soundly subdued by the brooding hedgehog. As he took his leave, Shadow called the captain "worthless". As he recovered, the ultimate mercenary realized, much to his horror, that he was afraid. The jackal then proceeded to throw a tantrum over how weak he was. Bitter about his defeat, the ultimate mercenary cast aside his old identity, going as far as to wear a mask to hide his face, in order to become stronger. He then obtained Eggman's finalized Phantom Ruby prototype, which granted him virtually limitless power. Eggman managed to fuse the ultimate mercenary with the Phantom Ruby prototype, creating the weapon he needed to defeat Sonic and conquer the world with. Reborn, the mercenary renamed himself "Infinite" and became Eggman's right-hand man in his conquest. Shortly after obtaining his powers, Infinite was dispatched by Eggman to deal with E-123 Omega, who had proceeded to slaughter a whole lot of Eggman's henchmen on his way through Eggman's base. Confronting Omega, Infinite effortlessly defeated the robot with his new abilities. Shadow soon after showed up at the facility to find Omega, and Infinite welcomed Shadow to their awaited reunion. When Shadow revealed that he did not remember Infinite however, Infinite proceeded undaunted to tell Shadow his backstory and what he had been up to since their first meeting a couple of months back. Once he was done, Infinite attempted to crush Shadow by trapping him in a virtual reality. Although Shadow broke free, Infinite was nonetheless impressed by the power he now possessed. After then hinting at his agenda to defeat Sonic, the facility he and Shadow were in began to collapse. Infinite, however, made his escape while cackling wildly.

Web Series

 * Jeff the Killer: Jeff was originally normal young man with surprising agility that his brother Liu willing to take blame over his fight against a trio of bullies until the same bullies incinerate his face alive in their next fight. Unable to cope with his injuries, he went mad and reduced into serial killer.
 * Salem: Salem was once a lonely girl locked in a tower by her cruel father until she was rescued by Ozma, a past incarnation of Professor Ozpin. However, after an illness took the life of her beloved she turned to the gods to revive him. After the near success, but failure, she was cursed with immortality, so she could never reunite with Ozma in the afterlife. Eventually gaining an army that spanned all of humanity, she challenged the gods only for humans to be wiped out with her as the sole survivor. Centuries passed and humanity returned from the dust, and Ozma was sent back to the world of the living, to try and deal with her. However after he told her of his mission, she decided the gods were no longer needed, and she alone would be all humanity needed for guidance. Ozma, realizing that his love had gone too far, attempted to run away with their daughters. A great battle was waged between the two, destroying their home and killing their daughters in the process. Salem murdered Ozma, and so began the centuries-long conflict between the two former lovers. For many centuries Ozma fought against Salem, trying to protect the Relics and find a way to destroy her for good.

Western Animation

 * Denzel Quincy Crocker: – As a young boy, Crocker happily lived in Dimmsdale with his fairy godparents. Unfortunately, after Timmy time travels to the year 1972, Timmy and Cosmo accidentally reveals Crocker's secret about his fairies in front of the whole town who had gathered to celebrate a day honoring Crocker. Because of this, Jorgen Von Strangle is forced to erase Crocker's memory of him ever having fairies, and because of an overdose from the memory wipers, Crocker lost his fairies and he became horribly disfigured, the town's people who had now completely forgotten all the nice things that Crocker did with his fairies assumed that they must be an angry mob and chased him down. He remembers nothing but he finds a DNA tracker device that Timmy left behind in the past on which he wrote "Fairy Godparents Exist" on the back before his mind was wiped, Crocker uses it to try and find the fairies.
 * Mojo Jojo: A chimpanzee named Jojo, Professor Utonium's hyperactive lab assistant who always broke everything he touched. He pushed the Professor towards a beaker of Chemical X, which caused an explosion, mutating his simian DNA, turning his skin green and causing his intelligence and brain to enlarge, growing out of his skull.
 * Dr. Claw: After an exploding cigar kills John Brown (Inspector Gadget) and destroying his car, a bowling ball coming from the fiery blast of the car crushes Sanford Scolex's hand, forcing him to replace it with a mechanical claw. Sanford Scolex is becoming Dr. Claw.
 * Lord Garmadon: Lord Garmadon used to be a human until being bitten by the baby Great Devourer where the said snake's venom ultimately corrode his mind and turned him into a black armored-clad, four-armed evil entity. It's later revealed how Great Devourer's venom corrupt Garmadon's mind and turned him evil like that was due to corruption within the Devourer's venom contained part of more malevolent being called Overlord.
 * Blight: Prior to his transformation into Blight, Derek Powers was a corrupt businessman who killed his own employee Harry Tully in cold blood to test a nerve gas that his company invented and ordered his subordinate Mr. Fixx to murder Warren McGinnis who learned about the gas; this led to Warren's son, Terry, to become the new Batman and stop Powers' evil plan to sell the gas to Kasnia. However, in the ensuing fight, Derek ended up exposed to the nerve gas; to make matters worse, radiation treatment intended to save Derek's life mutated him into a monstrous creature with glowing transparent flesh and a black skeleton.