Mickey Mouse. Currently: Either the Everyman and the cartoon character that everybody knows and loves, or the Keyblade-wielding Badass that Kingdom Hearts fans know and love. 1928: The guy who forced Minnie to kiss him, was also a bit of a jerk, and didn't mind harming his enemies.
Epic Mickey returns to his original characterization, sort of. Mickey's pranks set in motion the dangerous events of the game, and he has the option of either helping the inhabitants of the world he inadvertently endangered (becoming The Hero and looking more heroic), or looking out for himself and just trying to get back to his world (becoming The Scrapper and looking more sinister). Essentially, the player has the option of making Mickey like his modern self, or his original self.
Mickey in the Classic Disney Shorts was prone to almost Bugs Bunny-levels of retribution (such as his magical pranks on Donald in Magician Mickey), and had quite a low tolerance for things not going his way, notably pulling a gun on Donald in Symphony Hour when the Duck tried to ditch a Concert Gone Horribly Wrong.
In Daisy Duck's first appearance she was Donald in high heels; just like Donald she would get angry easily, and they even had the exactsameVoice Actor. Then she becomes the straight woman/voice of reason to Donald's Temper, a Deadpan Snarker in Quack Pack, and in House of Mouse, she becomes The Ditz. In early appearances she was quite mature and lady-like. Nowadays she's wild and ditzy.
Goofy went from Lovable Klutz to a period of being The Everyman in the 50s before being reverted back to the Klutz everyone knows and loves.
Huey, Louie, and Dewey were undisciplined troublemakers in their appearances up to and including the early episodes of DuckTales. Later on in DuckTales they're shown as quite responsible, almost never breaking the rules unless they think it's for a good cause. This change made the Five-Episode Pilot seem really weird when seen alongside later episodes in reruns.
Pete and Goofy's sons seem to have gone on a very bumpy journey before settling on the personalities they ended up with in Goof Troop, or even appearance—or in the case of Max, name. In The Everyman shorts mentioned above, the character who eventually became Max first appeared, but he was far more wild and uncontrollable. He's also "Goofy Jr." and for a while was a redhead with no ears. The character who later became PJ appeared in "Bellboy Donald" and he went from having everything in common with his father except being fat to... having nothing in common with his father except being fat. And his voice couldn't be more different either, going from gravelly and moderately low as a little kid to high, whiny, and clear, even as an adult.
Much like Flanderization, The Simpsons has this trope across the board, with the main character, Homer Simpson, serving as arguably the biggest example within this series:
Homer's most popular characterization as a crude, clumsy, lazy, ignorant man, with alcoholic tendencies, makes the first season's, "There's No Disgrace Like Home" an extremely odd episode to watch, especially for those who have never seen The Simpsons in its early days. In it, he is embarrassed by his family's boorish behaviour, including Marge getting drunk at his boss's party, and takes them to family therapy. If this was written after the first season, the roles would undoubtedly be reversed. Adding to this, Homer sells the TV in order to pay for the therapy; again, something he'd never even contemplate doing post-season one. While Homer is somewhat called out on it later that episode, since most of the things he was ashamed of them doing were his fault in the first place, he shows a lot more devotion to his family here than in later seasons.
Throughout the Ullman Shorts and most of the first season, she is a disrespectful troublemaker and not particularly bright, much like her brother. The writers conceived her and Bart as something of an interchangeable duo of bratty kids designed to drive Homer and Marge crazy. As Bart became the show's rascally Breakout Character however, Lisa as a female version of Bart seemed redundant, so they rewrote her as a brainy, yet socially awkward girl.
Lisa, in the early episodes, was a big fan of The Happy Little Elves while Bart preferred to watch Krusty the Klown and The Itchy and Scratchy Show (along with horror movies and, on the episode where Homer steals cable TV, X-rated movies). Later episodes either show both of them being childish, both of them being mature or, in a lot of cases, Bart being the childish one and Lisa being the more mature one.
Lisa's artistic side arguably dates back the development of the show, since her saxophone solo is part of the opening credits. Another case of this trope would be her rebellion against her music teacher Mr Largo. It's part of the opening credits, and is emphasized considerably in a couple early episodes. Later, not only did Lisa avoid conflict with her teachers to the point of becoming a grades-obsessed teacher's pet, but Mr Largo has been Demoted to Extra (and in some cases, Put on a Bus).
Early episodes showed Lisa being friends with other average girls in her class, liking ponies and having small sleepovers at her house. The later episodes established her as a sad loner who is very disliked, constantly bullied for being "smart", a very uppity Granola Girl and always trying to find friends outside her school and joins environmental groups and MENSA.
Supporting characters have gone through this too. When we first see Principal Skinner's mother in "The Crepes Of Wrath", she is the stereotypically sweet, frail old lady who embarrasses her son by calling him "Spanky." Afterwards, she was rewritten into a cruel matriarch who controls every aspect of her son's life. This could have had something to do with the cherry bomb incident in that episode though.
Skinner himself has changed. Whereas now he's a pathetic mama's boy who is usually easily outsmarted by Bart, in the early seasons, he was far more competent and authoritative, and his main shtick was a tendency to mispronounce long words (one of which was his own surname), have flashbacks about his days as a Vietnam War soldier and demonstrate his Green Beret skills, such as taking out a group of lawyers from The Disney Corporation who threatened to sue Skinner over using "The Happiest Place on Earth" for the school carnival. The writers kept the 'Nam flashbacks (though those got phased out as well as time went on), but ditched his penchant for mispronouncing long words, and eventually made him a loser who always fell for Bart's tricks.
Dr. Hibbert, in his first appearance, "Bart The Daredevil", is as a stern, competent professional. By his very next appearance, he became somewhat absent-minded and laugh-prone ("Ah-hee-hee-hee!") and an Expy of Bill Cosby, complete with a wife who looks like Phylicia Rashad (only with darker skin), a teenage son who looks like Malcolm-Jamal Warner, and a daughter who looked like Keisha Knight-Pulliam.
Police Chief Wiggum also went through a dramatic shift. In early episodes he is portrayed as a serious, no-nonsense police officer surrounded by idiotic officers. Later on, he becomes an idiotic police officer, whilst the others become somewhat smarter. Not coincidentally at all, this was around the same time the writers decided to make him Ralph's father.
Even before Ned Flanders became the Trope Namer for Flanderization, his personality had drifted towards being nice and meek. It's sort of funny to watch his first appearance, where he's so indifferent/oblivious to Homer's obvious financial problems that it reaches Jerk Ass proportions and he actually seems fully deserving of Homer's enmity.
Nelson and the Jimbo, Dolph, and Kearney trio used to scare Bart and were, overall, much worse kids. In fact, Nelson, in his first appearance, is so menacing that Bart has to use military tactics against him. Now they're all Bart's pals, with Nelson practically being one of the gang. That's not to say Nelson and the trio don't beat Bart up every now and then.
"One Fish, Two Fish, Blowfish, Blue Fish" features some supporting characters behaving in ways that seem extremely out of character in hindsight but were undeveloped or underdeveloped at the time. It features Lou and Eddie acting as incompetent or malicious policemen when generally speaking later on in the series they are portrayed as more reasonable, competent foils to their boss, Chief Wiggum. Additionally, Smithers sees Mr. Burns eyeing a beautiful woman and not only doesn't get jealous, but also encourages him and seems to be interested in the woman himself.
Randy Marsh's drift into Mr. Serious Business in the later seasons makes early episodes strange to watch; apparently World of Warcraft and Little League games deserve more panic than things like spontaneous combustion or lava engulfing the town.
In "Two Guys In A Hot Tub", Stan refuses to hang out with Butters and Pip because they are "melvins" and the geekiest kids in school. Whilst Butters and Pip are still Butt Monkey types in later seasons, Stan evolves into one of the nicest and most tolerant characters, while Butters practically becomes one of the gang, so Stan acting like he wouldn't be caught dead with them seems somewhat unusual. Even Kyle agrees with this point of view at the end.
Stan and Kyle actually were a lot nastier and more immature in the first couple of seasons, and actually seemed like genuine 8 year olds a lot of the time. It wasn't until around seasons six and seven that they became the eternal Straight Men and Only Sane Men to the idiocy of the wider South Park population.
The change is most noticeable in their treatment of other kids such as Butters. Originally Stan and Kyle were manipulative bullies only lower on the scale than Cartman; in the premiere "Jared Has Aides," all of the boys are seen bullying and exploiting Butters in an equal fashion. In subsequent episodes (despite getting thrown out of the gang), Butters seems to gain a more developed relationship with them as their more righteous tones take over. As early as in "Toilet Paper" a season later, they have resentment to exploiting Butters in a similar manner than they did before. Their nastier side occasionally returns, but they seem more ineffectual about it (cases such as "Pandemic" and "The Tale Of Scrotie Mc Boogerballs" where their manipulation backfires onto them).
Speaking of Butters, his character from when he first appeared is almost completely unrecognizable to his behavior nowadays. In his earliest appearances he was as much of a Jerkass as most of the other kids, and would gang up to pick on any other singled out boy (such as Craig in "Cartman's Silly Hate Crime 2000" when he gets made "the new Cartman" of the group). It's a far cry from the naive Nice Guy he quickly evolved into.
In the first four seasons, Eric Cartman was a whiny spoiled brat with a high scratchy voice who begged his mother into getting whatever he wanted and picked on Kyle mainly because he didn't celebrate Christmas, but the others got along with him for the most part, and he had many catchphrases. From season five onwards he is more intelligent, conniving, manipulative, and psychopathic; his voice is lower and deeper; he rarely whines or cries; the other boys hate him and rarely generally get along; and he doesn't say any of his catchphrases anymore. This is most noticeable in "Freak Strike"; Cartman is afraid he is not the most out-of-control kid on the show so he makes up a bunch of outrageous lies about horrible things he's done. Why would he have to make things up? What about the times he tried to reignite the Holocaust or partnered with Cthulhu… oh, yeah, those things happened in later seasons.
Remember when Wendy Testaburger was once a psychotic Yandere who murdered a substitute teacher Stan had a crush on? Compare that to the smart and sensible girl, who is even willing to break up with Stan, seen in later episodes.
The Mayor. In the early episodes she was the Queen of Town, only concerned about her own image while the other adults were smarter. In later episodes she's become smarter while everyone else got dumber, alternating between the primus inter pares of the adults' antics and the Straight Man having to deal with a town of idiotic citizens.
The town itself experienced this. In the early seasons, it was a small conservative mountain town, with a homophobic populace, only one police officer, and rednecks Uncle Jimbo and Ned playing major roles in many episodes. In the middle and later seasons, the town has grown significantly in size, featuring a Wall-Mart, a large community center, a two-story police station full of cops, a number of restaurants, among other things, Uncle Jimbo and Ned have largely been Demoted to Extras, and its politics have moved significantly to the left, to the point where it usually more closely resembles a Bourgeois Bohemian-filled liberal suburb than a conservative mountain town. This is currently Truth in Television throughout the United States, particularly in the West, as towns are growing larger and more "modern" thanks to the influx of migrants from the big cities. Matt Parker and Trey Stone are noted libertarian advocates, so their politics can swing from one Strawman Political to another pretty quickly.
Kenny went from being someone whose only purpose was to die horribly each episode to The Hedonist. That change may be a Justified Trope as him trying to live his life to the fullest, because he dies all the time, and really has no reason to avoid potentially life-threatening activities. (That and the fact that the creators have stated that the "Kenny dying every episode" trope had gotten stale and/or they had reached the point where they had trouble thinking of original deaths (almost) every episode. This was one of the reasons for the episode "Kenny Dies".)
Nearly every character in Family Guy has gone through dramatic changes.
Perhaps the most radical is Stewie. Once an egomaniacal baby genius, bent on world domination and matricide, Stewie has evolved into an effeminate, gay infant with a penchant for occasionally whipping out some manner of advanced technology.
In "If I'm Dying I'm Lying" Peter's blasphemous actions result in modified versions of the plagues of Egypt descending on Quahog. It is Brian who realizes the significance of the biblical events and when Peter insists "there must be a logical explanation" Brian slaps him repeatedly and states "Here's an explanation, GOD *slap* IS *slap* PISSED *slap*". Evidently dogs don't have the best memory because Brian later became an outspoken hard line atheist.
In Mayor West's first two appearances, he appears to be more of a Bunny-Ears Lawyercompared to the rest of the series. He's first introduced telling the story of the city's founding, and the humor is coming entirely from the ridiculousness of the (apparently completely true) story. On his second appearance when he meets Peter Griffin, he is actually surprisingly helpful until he discovers that Peter's property is not part of the United States. Then though, he reveals the trapdoor in his office (and his plans for further work on it), and his characterization is set.
Likewise, Glen Quagmire was initially portrayed as more of a 50s-type swinger fellow and seems quite normal in comparison to the extreme pervert he would eventually become; he was also very unsuccessful at attracting women before becoming the sort of guy who beds a different woman every night (often by immoral and illegal ways, such as roofies, an elaborate mechanism in his couch that sprays any woman who sits on it with knock-out gas, strips her clothes, and spreads her legs and lies her on her back while disco music plays [as seen and demonstrated in "It Takes a Village Idiot and I Married One"], and emotional manipulation). And even later than that, Quagmire still kept his near-rapist ways, but was shown to hate Brian with a passion (compare with some early episodes where Quagmire and Brian, despite not interacting much, can at least talk to each other without either of them wanting to kill each other), and actually care about two women in his life: his sister, who's being abused by her boyfriend, and Cheryl Tiegs, the one woman he loved so much, that he became a sex addict when she broke up with him.
It is also odd to watch the really early episodes where Meg was treated with respect and love by her family, like Peter trying his hardest to help her out at the school newspaper. Also when Meg and Chris are both in front of an air fan, Meg complains that Chris is hogging all the air to which he replies "Yeah well, YOU'RE hogging all the UGLY!" Unlike the later barrage of "Meg is ugly" jokes, this is merely intended as a childish insult someone like Chris would say to his sister.
Similarly Brian's first spotlight episode revolved around him being talked down to for being a dog. Lois chastises Peter for treating Brian this way and the family learn to treat Brian with dignity. Later episodes slowly make a Running Gag of the family manipulating or mocking Brain's forcive dog-like tendencies and at least once pointing he is semi human and disposable to them, usually with Lois herself being the most condescending and bullying towards him.
In Joe's first appearance, Meg hit on his son. He was slow to respond, but that was because she was so awkward. By the end of the episode, he seemed to genuinely enjoy her company. She also had a couple other boyfriends in the past. Compare to present day when boys will do anything to stay away from her, like commit suicide or murder a sibling so they can be too busy with an upcoming funeral.
In the earlier episodes Joe was a mild mannered wheelchair bound cop who is generally friendly towards everyone and well respected because he's crippled but capable. Later episodes have him constantly abused by Peter and other people due to being crippled, he has a severe anger problem often lashing out at and beating up his friends, and sometimes depicted as being depressed.
Also, in their first appearances, news reporters Tom Tucker and Diane Simmons were just two news anchors who may or may not have been attracted to each other, but the viewer wouldn't know, since their main schtick was being politically incorrect while delivering the news (like when Tom declared himself Jesus Christ or Diane mentioning a "freak heat wave" and Tom telling her that it was offensive towards his upside-down faced child). Through most of the show's run afterward, they dislike each other and constantly take shots at each other about how unattractive the other is.
In his first appearance, Mr. Panucci came off as an abusive jerk toward Fry. All future episodes portray him as one of the few people who actually cared about him (though he didn't show much concern when Fry was declared missing after getting pushed in the cryogenic freezer), seemingly retconning the first episode outburst as stress.
Kif is another notable example. In his first appearance he was a Deadpan Snarker who was clearly disgusted with Zapp's stupidity; the creators actually came up with him based on the question "What if Spock had hated Kirk?" In subsequent episodes he quickly evolved into an Extreme Doormat, however, miserably suffering under his boss' idiotic commands.
The Professor is a subtler example: in original episodes he had a sort of softspoken, kindly senility, while later he became prone to crazy outbursts and played up more Mad Scientist tendencies.
In the pilot episode, Fry is having a beer with Bender and asks why a robot needs to drink. Bender replies, "I don't need to drink, I can quit anytime I want." This statement comes across as peculiar in later episodes, where it's revealed robots use beer as a fuel source. Also, Bender in the first episode was defined by his depression, and he is first seen in line for a suicide booth, apparently having been driven suicidal when he found out that he was bending girders to make suicide booths. This is never brought up again, and in later episodes he becomes the loud-mouthed, obnoxious, jerk out to Kill All Humans that we all know and love. Explained by the electric shock he received which removed the inhibition that wouldn't let him bend anything without permission.
Another notable case is Zoidberg. Originally, he was shown as an incompetent doctor, yet still treated with the kind of respect one would expect of a doctor. However, after it was revealed that he was actually a good doctor if you're an alien, he morphed into an impoverished, kicked-around Butt Monkey.
Cubert, in his first appearance, was an Insufferable Genius who pointed out all the ridiculous aspects of the show. This, however, was not well-received and he became just a standard Bratty Half-Pint.
An unusual case of a one-shot gag character getting this: in an early episode, Fry meets a guy on the streets of New New York who replaces people's body parts. He is obviously a con-man, he offers to replace Fry's lungs with gills, but the gills only come a week after the lungs have been removed. Hermes meets him in "The Six Million Dollar Mon", but the man this time he actually makes the trades that Hermes offers him.
In their first appearance, Lrr and Ndnd are naked in their casual living room, only getting dressed when they go to bitch to Earth about one of their favorite shows being interrupted. Later episodes, while retaining their interests in Earth media, have them in their royal garb constantly and play up their evil overlord statuses, caring about significantly more important issues.
In later episodes, Roger has a surprisingly full, active life outside the Smith house, able to effortlessly conceal his identity as an alien through a variety of surprisingly effective, yet very obvious, disguises- which makes the early episode "All About Steve" strange to watch, where he is so desperate for human contact that the only place he can go to interact socially with others is at a sci-fi convention. A viewer coming to the series via the later episodes would no doubt be wondering why he doesn't just wear one of his 50,000+ disguises. Lampshaded in the commentary for "Roger Codger," the episode where Roger has to find his way from a landfill to home without being caught by the CIA, where they point out that the whole premise of the episode is somewhat worthless compared to his current persona. "Roger Codger" and some other earlier episodes also depict Roger as more beloved member of the family who, while with blatant Jerk Ass tendencies like the others, is actually willing to sacrifice himself to protect the Smiths. Compare this to later seasons which try to one up his self-obsessedComedic Sociopath persona with each episode.
Dale was also much more mellow (but still hated the American government) in the early days. Compare that to the insane conspiracy theorist in later seasons.
Even Bill was more calm and observant and less pathetic at first (even though he was still treated like a loser and constantly reminded that his life went to hell when his wife left him. Case in point: "Shins of the Father," when he was actually happy at Bobby's birthday until Dooley said, "Your wife divorced you"). After his habits and personality changed and years of Flanderization followed, it's hard to believe the Bill from the first episode is the same as that from later ones.
Hank is actually seen eating a charcoal-grilled burger in the first season, and actually admits it was the greatest burger he's ever eaten, despite being so in love with propane that he cares about it more than his lawn, his son, his niece, or even his wife. This would be unfathomable in later seasons, with his love of propane and hatred of all other forms of grilling/heating (one episode had him refer to butane as a "bastard gas"). Granted he probably said it just to be nice to Kahn, but even with that in mind it's still bizarre to hear him say good things about any fuel other than propane.
Bobby is also much different in early episodes. In the first couple seasons he was mainly a naive, kind of slow kid. By season 3 he started getting more development as a character.
Thanks to some of the most infamous cases of Flanderization in the animated business, a few of the title characters in the Looney Tunes shorts act very different in their 1940s and 1950s-onward appearances (Daffy Duck perhaps being the best example). Still, you will get a few rare nods to their original forms now and then (Space Jam, for example, tries to make a few of the characters' different personas more interchangeable).
Pepe Le Pew wasn't really French in his first appearance. The accent was a fake he put on to try to woo the ladies. Also, in Pepe's first appearance, he was married with children and cheating on his wife with a male cat who had painted himself up as a skunk so he can get back at the butcher who kicks him, the dog who attacks him, and the housewife who beats him. The difference between Pepe's first appearance and all subsequent appearances is more along the lines of Early-Installment Weirdness as Chuck Jones originally wanted to make Pepe Le Pew a One Cartoon Short Wonder, but when Eddie Selzer claimed that Pepe wasn't funny, Chuck decided to bring back the character and prove Selzer wrong.
Elmer Fudd originated in the late 1930s as a more bizarre Tex Avery creation known as Egghead, who was only once called Elmer Fudd on screen (in "A Feud There Was") before being retooled in 1940.
Crossing over with Early-Installment Weirdness, Sam the Sheepdog and Ralph the Wolf's first short, "Don't Give up the Sheep" had the two be typical slapstick villain and foiler, with Sam (named Ralph in this short) instead switching shifts with another dog named Fred. Later shorts introduced thedynamics the two are well known for. Also Ralph was very hairy and had menacing looking claws and fangs; later shorts had him looking identical to Wile Coyote but with lighter colored fur and a red nose.
In the first episode (and more so in the pilot), Phineas seems fairly irritable and sarcastic, apparently because the creators wanted him to seem like an annoying little brother. Within a few episodes he settled into his usual personality, chipper and laid back to the point of naïveté, which also worked to highlight Candace's paranoia.
Major Monogram. In season one, he was a very formal, authoritative no-nonsense boss who behaved in a totally cold demeanor to anyone he spoke to. Now, he's a One of the Kids eccentric whose mission briefings are never complete without at least one joke.
Before Revenge of the Sith premiered, General Grievous made his first appearance one year earlier in the Genndy Tartakovsky produced Star Wars: Clone Wars animated series. It is a very different characterization than what would end up in the live action movie; Grievous in the animated series is a scary, unstoppable killing machine that singlehandedly defeats a number of Jedi. In the movie, Grievous is less formidable adversary and who runs when he knows he cannot defeat an opponent. This characterization has continued into the CGI Star Wars: The Clone Wars.
Grievous tends to follow Dooku's advice in most of his later characterizations:
Dooku: Don't let your pursuit of trinkets cloud your reality. Remember what I taught you, General. If you're to succeed in combat against the best of the Jedi, you must have fear, surprise, and intimidation on your side. But if any one element is lacking, it would be best for you to retreat. You must break them before you engage them. Only then will you ensure victory and have your trophy.
Lucas hadn't decided at the time whether Grevious was going to be a warrior or a schemer. The Clone Wars team made him a badass for the first season, then were told that Lucas was going for the sneaky coward for the movies. Dooku's lecture and Windu crushing his chest were put into the second season specifically to bridge the gap between the two interpretations.
In her first couple of appearances, Susie was shown as something of a crybaby and was even more naive and boisterous as Tommy (her opening scene has her running into the room crying for her sucker, and then instantly forgetting all her sorrow to happily greet Tommy). Even in the early season(s), she begins to mature, and in most episodes after she acts as a Cool Big Sis and a more moralistic foil for Angelica.
Chuckie's fear of clowns is now legendary and one of his defining character traits. In the early season 1 episodes it was Didi who was afraid of clowns. The episode "Reptar's Revenge" has her freaking out when a clown sneaks up on her and Chuckie doesn't even bat an eyelid. Maybe he picked it up from her? Similarly later episodes demonstrated Chuckie's fear of spiders, despite acting rather nonchalantly towards Tommy's giant pet tarantula in "Spike Runs Away". All around Chuckie in early episodes was more a neurotic, curmudgeonly kid who was merely cynical to Tommy's adventures. It was only later on that was exaggerated into making him a paranoid Lovable Coward who feared anything and everything.
On that note, Chuckie is quite argumentative and disagreeable in the first season. From the second season onward, his character sweetens up quite a bit.
Phil and Lil didn't develop their Running Gag of frequently fighting over toys until the second season. Additionally their parents didn't settle into their more well known personalities until a few episodes in (Betty being a Lad Ette and Howard being a rather feminine man) - notably in "Touchdown Tommy" where Howard is happily watching football with the other dads.
In the first season Angelica would put on a sweet smile for the adults and have them fooled into thinking she was a well-behaved girl. She was also shown to have a low opinion of her father. Later episodes have the adults clearly not fooled by her schemes. Additionally she becomes a Daddy's Girl and it's shown that her parents are the ones she unambiguously cares for most.
When she was just a secondary character on Beavis and Butt-Head, Daria had a wider range of expression and a less monotone voice (in the early episodes) than she later had in her Spin-Off, and participated in extracurricular activities.
In season one Britney was shown as being a shallow, spoiled cheerleader who was definitely Book Dumb but not a complete ditz; later seasons upped the ditsiness, probably to accentuate her moments of ingenuity.
Jake, Daria's father, pretty much went the stereotypical route of fathers in sitcoms - at first he's not that dumb, just the only man in the house full of women and trying to deal with his messed-up childhood at the hands of his war veteran father, "Mad Dog" Morgendorffer and his passive mother who wanted to stand up to him, but couldn't. In the later seasons, Jake is beyond Bumbling Dad territory and is borderline Too Dumb to Live (and mostly rants about his messed-up childhood and cries over it).
In the first episode, a flashback shows that Archer once wanted to do something sexual that creeped out Cheryl. The same Cheryl who, as of episode 5, is established as a Nightmare Fetishist who is sexually aroused by murder and strangulation.
In early episodes, Pam was a sad, pathetic HR drone who can't get laid to save her life and even manages to convince Lana to sleep with her out of sheer pity. Come later seasons and she's suddenly the biggest Bad Ass in the entire cast and gives Archer the best sex he's had in his life.
The early pilot episodes of The Fairly OddParents had Cosmo as a fairy of normal unintelligence, and both he and Wanda were a bit spacey. (They described themselves as "two halves of one idiot!") In the actual series, Cosmo becomes a ditzyMan Child, while Wanda is the Only Sane Woman who seems to hold everyone else in contempt and always calls Cosmo out for being an idiot. This went through serious Flanderization over time. Plus the difference in voice: Cosmo sounded like a smooth-talking game show host in the pilot rather than the high-pitched Motor Mouth he became, which is odd, because it sounds like a case of The Other Darrin where Cosmo was voiced by two different people. In reality, Daran Norris' voice of Cosmo just changed overtime.
In the first episode, GIR is essentially a two-year-old with a larger vocabulary, completely useless and unable to focus on anything. While his attachment to reality remains non-existent, he is later shown to be productive and capable, able to accomplish many things (even if it is rarely anything that Zim wants).
Gaz was always easily annoyed and prone to violent threats, but in early episodes she never really acted on them—her very first line is swearing that Dib "will pay!" for drinking the last soda, but thirty seconds later she's talking to him civilly. Compare that to her insatiable desire for painful, terrible revenge in "Game Slave 2" or "Gaz, Taster of Pork."
The Tallests are a mild example—in the first episode they both have moments of intelligence and stupidity, but in "Backseat Drivers from Beyond the Stars" Red is the competent one and Purple is stupider.
The titular character of Dexter's Laboratory was quite serious and methodical, and at times a jerkass (mostly to Dee Dee), in the very early episodes. Compare this to the change in his character (which didn't occur after too long) that made him much more full of enthusiasm, giving him a more childlike, pleasant nature, though he was still an egotist. As for Dee Dee, all throughout the series her personality could be anything from the most insufferable Annoying Older Sibling to the Genius Ditz with more common sense than our resident boy genius.
Dr. Scientist on Jimmy Two-Shoes. In the first season, he was a rather helpful scientist who seemed rather friendly to Jimmy (even though he could feel exhausted by him) and was also established as Heloise's inferior. In season two, however, he suddenly Took a Level in Jerkass to become a villain, and it's stated that he won the Mad Scientist Award every year, easily beating Heloise.
The two main villains in Kim Possible. Drakken was originally a competent, and intimidating, person before turning into his typical Harmless Villain persona. Shego was just a typical mook, with few essences of her signature personality. Then they became Ensemble Dark Horse's and the team noticed how well Shego's voice actress worked with sarcasm.
In his first appearance on The Flintstones, Dino could actually talk, which never happens again in the series.
In X-Men: Evolution, Lance was originally a jerk ass with a known hair trigger temper and a small shade of manipulative bastard, and was to some extent a dark mirror version of Cyclops. In season two, however, they then established he had a crush on Kitty and pretended to be nice to get to her. After they broke up, he became the Jerk with a Heart of Gold that we all remember, who while willing to plot against the X-Men was also unable to leave a helpless old woman to die, and teamed up with them to stop an explosion. In fact, many don't even remember his original depiction, and if someone does point it out, its usually called just bashing him. Pietro, originally a Smug Snake, took over as the Brotherhood's leader with a BIG case of Manipulative Bastard who in all fairness, is the exact opposite of Cyclops. Only Blob and Toad really remained their original personalities, and there, Blob lost his anger, and Toad lost any competence he had (originally being able to hold his own against Nightcrawler).
They regain some of their comedic traits in the later half of the series, however they remain secondary foils to the Urpneys for the large part, compared to the pilot, where Rufus is clearly the center character.
The heroes were also a lot more smarmy and aggressive towards the Urpneys in earlier episodes, often favoring violent tricks and beat downs (sometimes even long after they'd already won). Later episodes made them more pragmatic and easy going, with Amberley even calling off an opportunity to punish an Urpney for trying to take the stone (something she often would have spearheaded beforehand).
Also in the first season, Urpgor was much more unhinged and somewhat decrepit (sort of like a traditional Igor), he also tends to be more consistently on the winning side of his rivalry with Blob, his boasting of having higher approval from Zordrak seeming to be somewhat true. Compare this to later seasons, where he is somewhat more lucid and cynical, and almost more of a Butt Monkeythan the other Urpneys.
In the pilot and several early episodes, Zordrak was much more collected and genuinely sinister, and from the very first scene was shown perfectly willing to back up his threats of deposing of incompetent Urpneys. As seasons progressed, he evolved into more of a traditional cartoon Bad Boss, having little role outside throwing demonic tantrums and issuing empty threats or slapstick punishments to his squad.
In the first season Stinky was a bully and sidekick to Harold who wore spiky wristbands. Later on, he's a sweet, naive Country Mouse struggling to find something he's good at. Since Stinky is much better known for how he was written in later episodes, it's a bit jarring to watch him in his earlier appearances.
Arnold himself went from being a Cloud Cuckoo LanderMr. Imagination to the Only Sane Man. One particularly notable example; Gerald and Arnold are having a sleepover, and it's Arnold who thinks his apartment is haunted while Gerald plays the skeptic.
In "Monkey See, Doggy Do" the museum curator tells Blossom that he didn’t want the police trouncing around looking for clues. Blossom finds the idea silly and she and her sisters conduct a reckless investigation. The curator faints after seeing the resulting damage to which Blossom fails to react. In later appearances she does all she can to preserve the arts and is horrified by any damage done to such institutions.
Francine was a lot more of a Jerk Ass bully in the early Arthur episodes, and Binkie was more of a straight-up bully then a sensitive boy with a Jerk Ass Facade.
In the original Teenage Mutant Ninja Turtles cartoon, April's co-worker at Channel 6, Vernon Fenwick, was originally part of her news crew who even helped her defy their boss in order to help her get an exclusive story on the Dimension X invasion. One season later, he's now a cowardly reporter who always tries to steal April's stories from her and is a gigantic suck-up and Yes-Man that would never dream of going against his boss. One possible thing that could have led to this evolution was his change in voice actors, the second one who notably gave him much more of a whinier voice than the original.
First introduced on Batman: The Animated Series, Harley Quinn was originally introduced as nothing more than a minor henchwoman working for The Joker, once muttering "Oy, beauty school is starting to look pretty good about now." after being caught by Batman. The producers envisioned her as a one-shot character, though she turned so popular that she became part of the Batman comics, which led to the comic "Mad Love", later adapted on BTAS, which revealed that she was an intern at Arkham Asylum who was seduced by the Joker during psychiatric sessions.
Thomas the Tank Engine has taken a few directions within the show's heavy run, starting off as an egotistical Bratty Half-Pint in Season One, before gradually maturing into a more responsible Nice Guy by Season Three. The HIT Entertainment seasons kept up the more altruistic image of Thomas, but granted back some of his childishness and naivete, and by the time of the CGI transition he has become something of a well intentionedCloud Cuckoo Lander.
Toby started off a fairly confident Big Brother Mentor, even being a tad snarky and acerbic with other more arrogant engines. As the series started branching from the books, Toby started gaining a meek, under confident side, and by the time of the CGI series is an almost childlike Lovable Coward that engines he previously tutored such as Thomas and Percy often end up soothing.
Similar to Toby, Edward started off as a Cool Old Guy and almost infallible Only Sane Man as in the books. Likely to avoid the same demotion he got later in them, the show's original stories made more attempts to give Edward a flawed side to enable more plots. These tended to be inconsistent for a while, in some he would be well meaning but insecure, while in others he would be arrogant and rude. By the time of the CGI transition he seems to have stuck as a toned down version of the former.
Season Seventeen seems to be reverting back a lot of the personalities for the classic cast (though Thomas still flip flops between characterizations Depending on the Writer).
Compare Rainbow Dash and Fluttershy's characterization in the episode "Dragonshy" and, well, pretty much any later episode where they interact in some form. In "Dragonshy" Dash pretty much seems to hate how meek and scared Fluttershy is, while in later episodes, she may be frustrated, but she is much more understanding of her friend's fears, and Fluttershy proves to be much braver and less jumpy in future episodes.
All of the Apple family to some extent. Applejack started off as a Hot-Blooded Calamity Jane-esque figure before taming into a more laid back Team Mom. Apple Bloom, originally Wise Beyond Her Years turned into the over excitable leader of the Cutie Marks (this is particularly jarring in "Bridle Gossip", where the latter acts an Only Sane Man to a growing paranoia concerning Zecora, that AJ is spearheading). Big Macintosh, who originally spoke and acted fairly normally, eventually became limited to his trademark "Yep" and "Nnnnope" outside sparse occasions and usually acts as a Not So Stoic in most of his appearances, while Granny Smith, originally a rambling decrepit old woman, became a still kooky but deceptively Cool Old Pony and, in opposite to Big Mac, began speaking full sentences.
Twilight Sparkle started off in the pilot (and a select few early episodes) as rather acerbic and aloof, and was thoroughly lucid outside her social ineptness. As she grew out of her Fish out of Water role however, her more subtle wackier traits became prominent, most of her spotlight episodes revolving around her status as The Finicky One. She also became a more consistently warmer and more excitable character, to the point of occasional Large Ham tendencies.
The Warden was introduced as a quirky yet sadistic type who gained entertainment from his inmates dying in gruesome ways, and that was said by the creators to be a super-genius that wasn't good with people. Compare the early characterization to the more outgoing Man Child who's willing to make friends, and that gets beat up and injured easily by his own inmates or others.
The Twins actually directly interact with the Warden in the pilot, and are shown to fear the possibility of being killed from the chaos they started. In later episodes of the series, they rarely mention him or are noticed by him. Their general personalities also shifted from being colder, a bit more callous and less verbose, to being more awkward and vulnerable. Their early meddling with the jail was also more often destructive.
Alice was much less verbal and more to-the-point with her dialogue, and seemed to be more threatening.
In Slade's first appearance he was a Card-Carrying Villain who spouted cliched dialogue ("Next time my planswill succeed- and the Titans will pay!"), smashed teacups when he got angry, and employed a butler. Later episodes turned him into the creepily emotionless Manipulative BastardTitans fandom loves to hate, gave his immediate Evil Plan a definite focus (though we never learned what his ultimate goal was), made his dialogue into what amounted to a series of very nasty Breaking Speeches and the butler was never seen with him again.note The Butler is named Wintergreen, and he was Slade's regular sidekick in the comics. He was most likely added to the first episode with the intention of developing into the same role in the cartoon, but was then dropped in favor of Slade working alone.
This happened to the third season's Big Bad, Brother Blood. In his first appearance he was hammy and egotistical, true, but he mostly overacted only when playing to an audience and could be quite calm and suave when he wanted to, and took his defeat at the end of the episode quite calmly. Later episodes made him into a much more hotheaded villain prone to outbursts of temper whenever things went wrong, and he largely lost his "Evil Professor X" shtick to become a much more straightforward Diabolical Mastermind. Also crosses over with Flanderization, as his obsession with Cyborg slowly ate up his entire character, to the point that his last appearance was entirely centered on stealing Cyborg's tech and upgrading his minions (and himself) with it.
Odd had a future-flash ability that he suddenly stops using for no reason half way through season one until the writers finally came up with a contrived explanation in a season three episode that basically amounted to telling the viewers that it was deleted for being a useless ability.
Xana's hornet monsters had an ability where they would spray an orange acid-like substance on the ground that would damage the Lyoko characters if they were near it. The ability was seen in only a few episodes of season one and was never used again afterwards.
William is, at first, seen to be able to swim just fine in the school's pool, yet when he's holding onto Odd for dear life when the two are dangling off a bridge...he claims that he can't swim.
A number of characters in The Amazing World of Gumball have changed from how they were in the first season, mostly in the case of other students of Elmore Junior High. For example:
Alan the balloon could act just as antagonistic to Gumball as some the other students, compared to the absurdly Nice Guy he later became. Him bopping Gumball on the head in annoyance in "The Mystery", for example, would be unheard of nowadays.
Sussie the chin puppet started off as a relatively normal student who, as she lacked usable arms, had trouble eating and doing homework. More recently, she's become a full blown Cloud Cuckoo Lander.
Nicole Watterson was a somewhat level-headed character with anger management issues to start with, but earned herself a need to always win at all costs starting with "The Fridge". (Effectively leaving Anais as the Only Sane Being in the process.)
At times, Darwin could be even dumber than Gumball (particually in "The Genius"), rather than typically being the brains of the two, if a bit naive.
The opening shows Courtney making sure exhaust from her Rolls Royce sprays in Ginger's face - something her actual character on the show would never do. It's likely she was conceived as a stereotypical Alpha Bitch but ended up becoming a Spoiled Sweet ditz who was more naive than actually mean-spirited. In fact, she becomes one of Ginger's closest friends over the course of the series.
Miranda goes from a manipulative, smug jerkass into a Jerk with a Heart of Gold at the end of the season. She's not kind, but she certainly wasn't as bad as she was in the older seasons of the show.
Eek! The Cat gives us Sharky the shark dog. Season one, he's a stereotypical Angry Guard Dog whose issues with the main characters were mostly territorial or otherwise just being a mean dog. Subsequent seasons, he was given more depth, started to become more mild-mannered eventually becoming the Only Sane Man. He also became sort of a Butt Monkey fallen victim into the zaniness of others. His mean-streak remains, but it's often provoked and justified.