Character Derailment examples in The Simpsons.
- Homer went from a well-intentioned buffoon who was fundamentally a good person under his many flaws to a hateful Jerkass who usually has little empathy for those around him.
- Marge went from a sensible, down-to-earth, and nurturing woman who was deeply supportive of her kids to a ditzy, snappy, and hypocritical housewife who has openly stated she would be much happier without her children.
- Bart went from an underachieving Brilliant, but Lazy prankster and troublemaker to a full-time sociopathic delinquent who can barely count to 10.
- Lisa went from an idealistic Child Prodigy who was still just a little girl at heart to an ultra-liberal, activism-obsessed, egocentric, dramatic mini-teenager with little sympathy for those who go against her beliefs.
- Maggie is mostly an average baby with a pacifier, but starting with "Who Shot Mr. Burns? Part Two", she exhibits a darker side in certain episodes (however, many fans consider this to be one of the better cases of Character Derailment, since Maggie Took a Level in Badass).
- Ned Flanders, when he first appeared, was a perfectly nice guy. He was religious and more than a little repressed, but he wasn't hurting anyone and he seemed to love all people unconditionally. In fact, the whole joke was that Homer hated him for no reason. He was the kind of neighbor most people would be lucky to have, friendly, kind and always willing to lend you whatever you needed. Then came his Flanderization, where he went from a generally nice guy to his ludicrously meek, inoffensive, and Christianity-obsessed persona. The derailment kicked in later, when the Simpsons writers decided they wanted a Right-Wing Christian Strawman to mock and so they derailed Flanders to make him fit the bill.
- And maybe this is more Early-Installment Weirdness than character derailment, but in Ned's very first appearance he was so thoroughly insensitive to Homer's obvious financial troubles that he came across as a complete Jerkass fully deserving of Homer's enmity (though Ned may not have been aware of just how bad Homer's financial problems were).
- In fact, some recent episodes show that the derailment has effectively inverted the Ned-Homer dynamic, as now Homer is a happy-go-lucky idiot with Ned loathing him effectively just for existing. One episode actually covers this, in that Homer realized the reason he hated Ned was because he always found him better than him and moved on, while Ned's reasons to resent Homer in later seasons is that Homer keeps calling him Stupid Flanders within earshot of him and demeans him in front of Rod and Todd, they do end up making amends, though.
- C. Montgomery Burns is a big victim of Villain Decay. In early seasons, Burns was a downright sadistic and evil old miser who generally treated his employees like crap, stole from children, tried to block out the sun (for money), violently mutilated sea animals to make Lil' Lisa Slurry and planned on turning a litter of puppies into a fur coat. Turn to later seasons and he's just a feeble old man who is more ineffectual than anything else and serves more as fodder for jokes about being behind the times then anything else. Although every now and then he gets a Forgot Flanders Could Do That moment and ends up doing plot such as launching his environmental hazards on the Amazonian forest or putting Mona Simpson on the run from justice out of spite.
- Patty and Selma have shown a most extreme case of derailment than anybody else in the show. They were originally just a couple of gruff curmudgeons who hated Homer and think Marge should divorce Homer, take the kids with her, and remarry. Later seasons would add appalling housekeeping and near-criminal incompetence at their jobs (both arguably even worse than Homer's), not to mention smoking everywhere, including around children and on the job at the DMV (which nearly gets them fired — until Homer takes the fall for the both of them). Selma would go through three astonishingly bad marriages (and she only wised up after realizing how long her last name was), while Patty became a full-fledged militant lesbian (despite that "Principal Charming" established that Patty is heterosexual and willingly celibate, while Selma has had celibacy thrust upon her and wants to have a husband and kids before she dies alone and unloved). Of course, all this pales next to becoming a new contender for "Most Violent Simpsons Characters", being utterly obsessed with trying to end Homer's marriage, including celebrating his death by buying a tombstone for Marge, trying to kill him by pushing him off a bridge (though that was part of Homer's plot to land on the boat where his "Congratulations on Completing Community Service" party is being held, the fact that Patty and Selma were willing to kill Homer just because is unsettling) and attempting again later by reenacting the infamous Bathroom from the first Saw movie.
- Moe is also worth a mention. When he first appeared, he was merely a surly and cynical bartender, who was a pretty decent guy despite his rough edges. In later episodes, he's a miserable wretch and registered sex offender who conducts numerous illegal operations, tries to kill himself every other episode, and constantly lusts after women in revolting manners.
- Otto counts too. The character was originally depicted as a laidback youth who got along great with kids and was generally a really fun guy to be around, despite his humble status as a bus driver, his carefree nature, and the occasional hint that he was a pot smoker. Later on, he devolved into this wretched and dangerous lowlife with an insane addiction problem to any illegal and hazardous drug he can get his hands on — a trait gets brought up every time he appears now and almost entirely defines his character in post-Golden Age seasons.
- Principal Skinner was a more rounded character early on. While still meek towards his mother and Superintendent Chalmers, this was balanced out by occasional reminders that he had been a Green Beret in the Army and could be badass when needed (such as when Bart played hooky.) These got dropped and his doormat behavior played up, with pretty much anyone being able to push him around easily. He was also more passionate about his job and upset with the constant budget issues that plagued the school. Now he’s the one in favor of budget cuts, making him the source of most major conflicts that happen with the school.
