The Simpsons has been running for 33 seasons, with over 700 episodes. Even with a well-stocked series bible, the writers are left with hundreds of characters. Each character has their own backstories, character traits, and plotlines. Keeping it all straight can be nearly impossible, and The Simpsons has never been immune to retcons, intentional or accidental.
Often, there is a deliberate wrench thrown in a character's backstory for the sake of an episode. Sometimes, one-off jokes contradict one another. Either way, there are several times when The Simpsons has been seemingly unable to avoid retconning itsself.
8 The Nature Of Homer And Mona Simpson's Relationship
A big part of Homer Simpson's backstory is that he was raised by his father alone, having believed that his mother died when he was young. Mother Simpson involves Homer reuniting with his mother, Mona. A major part of Mother Simpson is Homer learning for the first time that his mother is alive.
Mother Simpson is considered a standout episode, and one of The Simpsons' best. In season 33, Mothers And Other Strangers reveals that Homer met Mona at least twice between her disappearance and her first appearance in The Simpsons. Once when he tracked her down at sixteen, and once when Bart was born. As such, Mother Simpson makes far less sense.
7 Ned Flanders' Age Changes
The ages of many of the side characters on The Simpsons is left largely ambiguous. Bart and Lisa's fellow students are their age or teenagers, Homer's colleagues are various adult ages, but few concrete numbers are given. In Viva Ned Flanders, the Simpsons' neighbor Flanders is revealed to be 60 years old, despite his youthful appearance.
This is treated as a major revelation, and inspires Viva Ned Flanders' main plotline. However, it contradicts previous details given about Flanders. This includes Flanders being a young child in a flashback to 'thirty years ago', marking it as a clear retcon.
6 Marge And Homer In The '90s
The Simpsons tends not to acknowledge its sliding timeframe. The Simpson has progressed from the '90s to the 2020s with Bart and Lisa remaining kids, Homer and Marge remaining in their 30s, and Maggie remaining a baby.
Nonetheless, That '90s Show engages directly with the sliding timeline. That '90s Show flashbacks to Homer and Marge's early relationship, having been widely-accepted as happening in the 1970s - a date that no longer works with The Simpsons' present day. In addition, it changes the early circumstances of Homer and Marge's relationship to include a breakup, and Homer inventing the 'grunge' genre.
5 The Circumstances Of Nelson's Father Leaving
Several characters in The Simpsons have missing parents, with one of the more notable being Nelson Muntz. Nelson, for a long time, believed his father had 'gone out for cigarettes' and never returned. The clear intent was for the viewer to assume that his father, Eddie, had run out on the family.
In Sleeping With The Enemy, however, Bart finds Eddie Muntz in a circus. Eddie gives the improbable explanation of having been separated from his family by being confined to the circus. This is clearly not the original intent behind the character - especially when he runs out on his family again in a later episode.
4 The Shifting Age Of Mr. Burns
Not all of the retcons in The Simpsons are mistakes or attempts at new plotlines, sometimes they're just improbable jokes. As one of the main villains of The Simpsons, the consensus for the age of Mr. Burns is simply 'very old'. He has been identified as being in his 80s, and as several ages above 100.
In other episodes, however, Mr. Burns is portrayed as far older. His age has four digits, and his birthplace listed as 'Pangaea', a supercontinent hundreds of millions of years old. As such, for a joke, The Simpsons is not afraid to retcon Burns' nature.
3 Moe's Constantly-Changing Early Life
It would be difficult to draw a coherent backstory for any character in The Simpsons with more than a few episodes to their name. It is far harder for Moe than for many others. Perhaps as a joke, The Simpsons frequently gives contradictory (and often demeaning) information about Moe's background.
Moe has been hinted to be a Dutch immigrant, Armenian, Italian, Tibetan, a native New Yorker, and other nationalities. In addition, he is said to have been abandoned as a child at a summer camp by his family. Yet, a major plotline also recounted him falling out with his father as a teenager over the family business. With many other contradictions, The Simpsons seems to reject attempts to give Moe a true backstory.
2 Carl's Icelandic Nationality
Despite his reasonably large amount of screentime as one of Homer's friends, Carl Carlson has been rarely-explored, almost never being the focus of an episode. Nonetheless, hints at his backstory suggested that had been raised in Springfield alongside Homer and Lenny, with a black family.
The focus episode The Saga Of Carl, however, reveals that Carl was raised in Iceland by an adoptive white family. He only moved to Springfield later in life. Although it served The Saga Of Carl's plot, the retcon made several previous episodes - especially flashback episodes - hard to reconcile.
1 The Armin Tamzarian Reveal
One of the most notorious episodes in the entire run of The Simpsons is The Principal And The Pauper for the sweeping retcon it introduces to a major character. It runs on the idea that Principal Skinner is not the man he says he is, but an imposter named Armin Tamzarian who stole his Commanding Officer's life.
This reveal was reviled for making Skinner a far less sympathetic character, for its clumsy handling, and for being impossible to reconcile with several flashbacks from Skinners's past. The Principal And The Pauper is widely-disliked. The Simpsons has all-but ignored the retcon ever since.