History TookALevelInDumbass / WesternAnimation

* ''WesternAnimation/AmericanDad'': Ever since Season 9, Stan Smith slowly seems to lose more and more brain cells to the point where a more "subtle" name for him as this point is Peter Griffin II.

* ''Franchise/Ben10'': while Ben was immature and bratty in the original show, this was justified due to him being a 10-year old kid. When the sequel ''WesternAnimation/Ben10AlienForce'' turned him into a teenager, he TookALevelInBadass and became much more competent, smarter and responsible. Then in season 3, the writers tried PanderingToTheFanbase in a failed attempt to make him more like his 10 years old self, and he started acting more narcissistic and cocky again. Partially justified in-universe in that saving the Universe went to his head, but it sticks far longer than it should. This was then zig-zagged in ''WesternAnimation/Ben10UltimateAlien''. Finally, ''WesternAnimation/Ben10Omniverse'' took the trope to {{Flanderization}} levels on both his teenage self ''and'' his 11-year old self, making them both much more bumbling, clumsy and immature while removing a large amount of his badassness from ''Alien Force''.

* ''WesternAnimation/FamilyGuy'': Peter Griffin was a dumbass, to begin with, yet he was a good guy at heart and after discovering how much trouble his idiocy caused would do his best to fix it. After the first [[UnCanceled uncancellation]], he's gotten even worse. He's legally mentally challenged in-canon. You never would have seen that coming in the show's early seasons. Taken to extremes in "Brian's a Bad Father", where Quagmire calls Peter out for foolishly shooting him in the arm during a hunting trip. Heck, now he can't even walk and chew gum ''at the same time''.

* This happened to Fry in ''WesternAnimation/{{Futurama}}''. In the earliest episodes, where he was supposed to be a FishOutOfTemporalWater and stories would mostly focus around him adapting to life in the 31st century, he was a fairly average guy with a dash of {{Cloudcuckoolander}} and a few moments of genuine cleverness. As the show progressed, he adapted to his surroundings much faster than the writers intended, and so he devolved into a gibbering manchild [[PingPongNaivete unless the writers needed him to say something profound]].

** Discord has become less intelligent ever since his debut. Initially introduced as the vile master of chaos, his next appearance had him eagerly play along with Fluttershy's submissive attitude and do idiotic things just to make her happy. Despite how he also TookALevelInKindness, him promising to only use his powers for good is obviously what leads to VillainDecay. As one will have observed, the entire purpose of the villains' evilness degradation is too make Lord Tirek the BigBad instead.
** Poor King Sombra... Despite being a FlatCharacter in his debut in Season 3 – he nevertheless stood out for being a dangerously savvy NoNonsenseNemesis compared to the other, more–VillainBall-prone antagonists. But come Season 9, and he finally got more characterization – now as a reckless SmugSnake who monologued his head off, got overconfident at the drop of a hat, and basically caused his own (final) defeat.

** Homer Simpson has never been the brightest bulb in the box, but he actually started out a fairly normal person (particularly in the Tracey Ullman shorts, back when his temper was his defining character trait). The trend towards increasing dumbassery was so noticeable that more than once there have been in-show explanations for this, all contradictory. Creator/ConanOBrien said on a DVD commentary that Homer's IQ started out at 65 and dropped 5 points a year until it hit zero in Season 13.
** Much like his father, Bart has become increasingly stupid in recent seasons. In earlier seasons he didn't do well in school mainly because he didn't care and he couldn't stay focused for long periods of time but he was brilliant in other fields as he could manage to pull off time-consuming schemes and pranks in minutes, could master languages in relatively short time, and was a skilled detective. (At one point he was quite plausibly diagnosed with ADHD, but this was used for a one-episode plot about overmedication and then never mentioned again). In more recent seasons he's so stupid he can barely read or write, is easily entertained, and has trouble figuring out simple tasks.

* WesternAnimation/SpongeBobSquarePants has always been [[{{Cloudcuckoolander}} a little loopy]]. But he has become actually dumber and dumber (not just loopier and loopier) as the series has progressed, especially in "A Pal for Gary".

** This trope also applies to [=SpongeBob=]'s best friend, Patrick. Oh so much... Though, truthfully, how much dumber can you get after mistaking mayonnaise for a musical instrument, or forgetting that you ate a candy bar literally ''two seconds later''?

** Darwin's intelligence took a nosedive in Season 6, despite serving as his brother's StraightMan in Seasons 2-5. In "The Brain", a doctor states and shows a chart showing that Gumball is smarter him. In "The Potion", it takes him a while to figure that Gumball wants to use a shrinking potion on Hector despite many hints, and mistakes the "O" in orangutang as a zero. In "The Understanding", he thinks that have a piece of a wire on him is the same thing as "wearing a wire".

* In the 1965 version of ''WesternAnimation/SecretSquirrel'', Morocco Mole was a BumblingSidekick. In the 90's revival, ''Super Secret Secret Squirrel'' (made for ''2 Dumb Dogs''), he's TooDumbToLive.

** Darwins intelligence took a nosedive in season 6, despite serving as his brothers StraightMan in seasons 2-5. In "The Brain", a doctor states and shows a chart showing that Gumball is smarter him. In "The Potion", it takes him a while to figure that Gumball wants to use a shrinking potion on Hector despite many hints, and mistakes the "O" in orangutang as a zero. In "The Understanding", he thinks that have a piece of a wire on him is the same thing as "wearing a wire".

** Cameron goes from being able to realize everything regarging Mike's [[SplitPersonality splite personalities]] in ''Revenge of the Island'' from mere observation to not being able to realize Mike's body was took over by Mal in ''All-Stars''. This is painful because he's usually TheSmartGuy.
** Similarly, while Zoey was fooled by Scott in ''Revenge of the Island'', she was intelligent enough to realize something three persons tell her... something that is gone by the time of ''All-Stars''. It seems that the writers did this on purpose, considering how both her case and Cameron's are regarding them not knowing about Mal.

* The titular Johnny from the Danish series ''Soldier Johnny'' is a rather extreme example. At the start of the series, he is more of a StereotypicalNerd - quite [[NerdsAreNaive gullible]] and occasionally [[AbsentMindedProfessor absent-minded and forgetful]], but never outright stupid. He's also very good with technology, especially computers. With time, as the show becomes more action-oriented, his intelligence takes a steep nosedive, and he becomes more and more incompetent at relatively simple tasks. He still remains a tech whiz, but he seems more like an IdiotSavant (with emphasis on the "idiot" part) than a nerd. In the last season of the series, he has become so absurdly stupid that he can't even put on his own pants without guidance, he often only communicates by making nasal sounds and yelling his own name rather than saying actual words, and he even breaks a television screen (that his friends were watching a movie on) to "free the little people trapped inside the box", showing that his last speck of intelligence - being good with technology - is also gone.

* The titular Johnny from the Danish series ''Soldier Johnny'' is a rather extreme example. At the start of the series, he is more of a StereotypicalNerd - quite [[NerdsAreNaive gullible]] and occasionally [[AbsentMindedProfessor absent-minded and forgetful]], but never outright stupid. He's also very good with technology, especially computers. With time, as the show becomes more action-oriented, his intelligence takes a steep nosedive, and he becomes more and more incompetent at relatively simple tasks. He still remains a tech whiz, but he seems more like an IdiotSavant (with emphasis on the "idiot" part) than a nerd. In the last season of the series, he has become so absurdly stupid that he can't even put on his own pants without guidance, he often only communicates by saying nasal sounds and yelling his own name rather than using actual words, and he even breaks a television screen during a movie to "free the little people trapped inside the box", showing that his last speck of intelligence - being good with technology - is also gone.

** Cosmo most definitely. His first appearance was of a suave, gentlemanly persona in the first episodes, who made sarcastic comments and wisecracks. Now he's a screeching, literally brainless fairy who would have already killed Timmy if not for his wife's constant surveillance.

** This got toned down a little as of Season 9B, thanks to CharacterRerailment from Stephen Hillenberg coming back to the show.

** Homer Simpson has never been the brightest bulb in the box, but he actually started out a fairly normal person. The trend towards increasing dumbassery was so noticeable that more than once there have been in-show explanations for this, all contradictory. Creator/ConanOBrien said on a DVD commentary that Homer's IQ started out at 65 and dropped 5 points a year until it hit zero in Season 13.

* The titular WesternAnimation/JimmyTwoShoes in season 1 was an airheaded and oblivious fellow, but he was shown to have genuine moments of cunning [[TheCloudCuckooLanderWasRight (if odd ones sometimes)]]. [[DependingOnTheWriter Some writers]] went even as far as making him the StraightMan to [[FatIdiot Beezy]] and [[MadScientist Heloise]]. In season 2, he's as dumb as Beezy, even more childish and oblivious, and more prone to making things worse due to his own idiocy [[UpToEleven than ever]] with not a single moment of intelligence in sight.