Start Of Darkness / Western Animation

• The Arthur episode "The Last Tough Customer" shows Molly's in The Teaser: when she was in maybe kindergarten or first grade, a couple of older kids teased her about her poofy hair. She took out her hairbands, letting her hair fall across her eyes, and became a bully.
• Avatar: The Last Airbender: "The Storm", aside from telling how Aang ended up frozen in an iceberg, gives us how Prince Zuko got his scar and banishment; he spoke out against a general who believed We Have Reserves, but because it wasn't his place to speak out, he had shown disrespect, and the Fire Lord declared a duel to resolve the matter. Zuko accepted, thinking he'd fight the general, but because it happened in the Fire Lord's war room, it was the Fire Lord he'd disrespected. Zuko couldn't fight his father, and begged forgiveness. Instead, he got a fireball to the face and an exile that would not be lifted until he found the Avatar, considered a Snipe Hunt at the time.
• Batman: The Animated Series:
  • Temple Fugate, a Schedule Fanatic, decided to take a break from that schedule at the suggestion of then-Counselor Hill and things went horribly wrong, costing him a court case. Temple snapped and vowed revenge on Hill, now Gotham's mayor, becoming the titular villain of "The Clock King". He orchestrates a smear campaign against Mayor Hill as a prelude to kidnapping him and putting him in a Death Trap.
  • Edward Nygma created a computer game that made millions but was then fired by his publisher so that, as according to his contract with them, he would't get anything from it. Thus, in "If You're So Smart, Why Aren't You Rich?", Nygma becomes the Riddler in his attempt to punish his old boss. Notable in that this is one of the few episodes where the Villain of the Week escapes, unharmed and untouched. He was never there to be caught. In the ending, the wealthy businessman heads to bed. Shaking in terror all the way, he locks the multiple locks on his door, climbs into bed with a double-barreled shotgun, and is too paranoid to sleep.
  • The tie-in comic book for the series, The Batman Adventures, describes (but does not show) one for Arnold Wesker, a.k.a. the Ventriloquist. The Ventriloquist tells Batman that he was actually born into a mob family and was encouraged by his mother not to allow himself to drift into a life of crime like the rest of the family had done. Arnold promised her he'd do this... but then his mother was killed one night by a bullet meant for his father, and Arnold felt that he had to avenge her. Even after becoming a gangster, he still kept a framed photo of his mother on his person at all times — until Scarface, in a fit of jealousy (because the Ventriloquist had been keeping company with other puppets in an attempt to distance himself from Scarface), tore up the photo, causing Arnold Wesker's mind to snap for good.
  • The Batman Adventures' "Mad Love" and its later TV adaptation gives one to Harley Quinn. Originally Harleen Quinzel, she was a young, new therapist at Arkham Asylum hoping to make a name for herself treating the patients there, starting with the Joker. Unfortunately, Joker's mind games and manipulations slowly turned her into the mad moll we all know.
• BoJack Horseman: It's long been obvious that a large part of the titular character's issues came from the abuse suffered at the hands of his resentful and bitter parents Beatrice and Butterscotch, who play a sort of Greater-Scope Villain to his issues. Season 4 greatly expands their own backstories, particularly Beatrice Horseman's, showing that Beatrice Used to Be a Sweet Kid up until her happy family broke apart after her brother's death in World War II, which caused her mother to go insane with grief and get lobotomized, after which Beatrice underwent a traumatic bout with Scarlet Fever and had to deal with being raised by her abusive and sexist father. This drove her into the arms of charming amateur writer Butterscotch, but a surprise pregnancy ensued, causing them to move to San Francisco, where their lack of money and Butterscotch's failed attempts at achieving success with his writing make them grow bitter towards each other and little BoJack, whom they would use as an outlet for their issues.
• In Darkwing Duck, an episode is dedicated to the origin story of Reginald Bushroot, and how he became a villain.
• DuckTales (2017):
  • "The Ballad of Duke Baloney!" features the origin story of Scrooge's fierce business rival Flintheart Glomgold. In his youth, he was a South African shoe-shine boy named Duke Baloney, and Scrooge offered to give him his own #1 Dime in hopes of inspiring him. However, Duke took it as an insult that the richest duck in the world would short-change him and, after stealing a money clip containing a million dollars in cash, vowed to get even by becoming the new richest duck in the world. The newly christened Flintheart Glomgold became determined to out-do Scrooge in everything, including being Scottish, which is why he adopted a Scottish persona.
  • "The Duck Knight Returns!" does this for Negaduck. Jim Starling was the actor for the Darkwing Duck TV series in-universe. However, when a movie was being made, the decision was made to replace him with a new actor. Being a tad egotistical, he went crazy and attempted to take over the movie and kill his replacement. The end result led to set exploding and Jim, believing that it was all the replacement's fault, embraced his evil side. Oh, and the replacement? A young Drake Mallard, who is convinced by Launchpad to be the real Darkwing Duck.
• The Fairly OddParents!: In the episode "The Secret Origin of Denzel Crocker!", it is explained how Crocker became obsessed with fairies and why he's so bitter toward his students and life. It's due to Timmy accidentally costing him his fairies (ironically Cosmo and Wanda in the 1970s) when he travels back in time to discover what made Crocker so bitter. Naturally, Crocker doesn't remember this but before his memories were erased, he had time to scribble down "fairy godparents exist" on a magic detector he managed to hide, leading to his lifelong obsession with proving their existance.
• The Moral Orel episode "Passing" for Clay Puppington. We see him as a child, when he discovers that his mother miscarried ten times before he was born, he becomes upset and briefly fakes his own death which causes his mother to have a heart attack and die. This puts him at a distance with his father, who Clay intentionally tries to provoke into hitting him so he'll be "worth it".
• In the alternate universe in the Justice League episode "A Better World", President Lex Luthor had Flash executed, and then taunted Superman about the fact that, since Superman historically wouldn't kill or otherwise do anything more than have him incarcerated, he would basically get away with it, as always. This prompted Superman to cross the line and kill him, thereby starting the Justice League on the path to becoming the Justice Lords.
• Miraculous Ladybug: Gabriel Agreste learns Emilie is dying as consequence of her using the Peacock Miraculous and refuses to accept her impending death, causing him to shut down emotionally.
• Implied with Emperor Belos in The Owl House. What's been seen of his backstory indicates that back when he was known as Philip Wittebane, he was deeply influenced by the normal views of his time period into seeing witches as beings to be feared and hated, leading to him being naturally antagonistic towards the denizens of the Boiling Isles. A closer look into his memory portraits reveals that he used to have an older brother named Caleb whom he was very close to until the day a witch entered into Caleb's life. The episode "Thanks to Them" reveals that Caleb had gone with the witch to the Demon Realm and fell in love, while Philip had gone on after his brother to find and retrieved him. Finding out that they eloped angered Philip due to his anti-witch beliefs, and the two brothers fought, which led to Caleb's death. This incident is implied to be the driving force for Belos' genocidal plans and the Grimwalkers, as he's still haunted by that memory in spite of his sociopathic attitude in present day.
• In Rick and Morty, we finally get to see Evil Morty's in the flashback at the beginning of "Unmortricken": his Rick was far more of an abusive Jerkass to him than the main Rick of the series is to the main Morty, and after he—originally just a normal Morty—was justifiably annoyed by their latest gross, humiliating adventure (which involved him having to "go up an ass"), his ungrateful Rick just went off on him for "whining" and dared him to quit if he didn't like it. This was the last straw for Morty, who decided to do exactly that: he permanently dropped his stutter, pretended to smooth things over by giving Rick enough beer to get him drunk, and donned his newly-perfected eyepatch to become the Evil Morty we all know, attacking the now-wasted Rick and putting him under Mind Control to turn him into the Evil Rick first seen in "Close Rick-Counters of the Rick Kind".
• The Simpsons: Parodied in the episode "The Seemingly Never-Ending Story". In Moe's story-within-the-story, it's revealed that Springfield's recidivist criminal Snake Jailbird used to be an Adventure Archaeologist until he came into Moe's Tavern. After Moe steals his Mayan coins, Snake declares "I'll take my revenge on society — by which I mean convenience stores."
• Star Wars: The Clone Wars shows the events that made Anakin Skywalker a hero of the Clone Wars. But sprinkled throughout are moments foreshadowing his fall to the Dark Side. More than once, he Force-chokes his enemies to save Ahsoka or Padmé's lives. His trust in his master is shaken when Obi-Wan fakes his own death and does not tell Anakin. And his faith in the Jedi Council is shattered when they turn their backs on Ahsoka.
• Tangled: The Series gives us alchemist Varian, who has a start of darkness in "Queen For a Day" after his father is encased in a combination of his own mixtures and the black spikes popping up around Corona. As a direct result of Rapunzel's reluctant refusal to help Varian due to the kingdom facing an Endless Winter, his optimism is replaced with hardened cynicism and he goes from happy, eager-to-help child to one of the series' darkest villains.
  • It is revealed in the episode Rapunzel's Return that Cassandra's biological mother was freaking MOTHER GOTHEL, who never gave her daughter any attention or love, and when Gothel discovered that Rapunzel's hair carried the magic of the Sundrop flower, she abandons her to kidnap the princess, leading to Cassandra being adopted by the captain of the guard. When she discovers this in an earlier episode, she backstabs the group by stealing the Moonstone as she blames Rapunzel for Gothel leaving her; Rapunzel lampshades that she was a BABY when it happened and therefore had no say in the matter.
• The Transformers: Animated episode "Along Came A Spider", where we find that Blackarachnia's hatred against Autobots began when Optimus Prime and his friend Sentinel accidentally left her behind on an alien planet inhabited by spiders. While still inside the caves, Blackarachnia is accidentally mutated into a technorganic spider, causing her to join the Decepticons as revenge for Optimus and Sentinel's betrayal.

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