In the 2008 adaptation of Horton Hears a Who!, Rudy is altered to be much more social and skeptical of his mother's extremely uptight and arrogant worldview. While in the original short story his role consisted of merely echoing his mother's "Hmph!", in the film he is in fact the one who saves the clover and all of Whoville from falling into the boiling beezlenut oil.
In Mask of Light, the protagonist Takua was written as a irresponsible, goofy and rather dim to contrast with Jaller's Straight Man, whereas in previous and arguably every other incarnation he is an adventurous Guile Hero.
Also from Mask of Light, Onua, who has always been depicted as quiet and wise, was instead depicted as a typical dim-wittedBoisterous Bruiser. Fortunately, further adaptations returned to his original characterization.
Web of Shadows changed Sidorak from a fierce Warrior King who personally leads his army into battle to a coward who is described as never dirtying his hands with combat.
In The Jungle Book (1967), Baloo and Bageehra essentially switch personalities (Baloo was a stern mentor and Bagheera was a laid-back friend in the book), Kaa becomes a clownish villain rather than a wise mentor for Mowgli, and Shere Khan is turned from a Smug Snake to a Faux Affably Evil villain.
In The Little Mermaid, the Sea Witch becomes a cunning, dishonest, power-hungry villain who tricks Ariel into signing a contract with her, rather than the neutral character in the original tale who warns the mermaid of the consequences of her magic. Also, the mermaid in the original story is a demure Shrinking Violet, repeatedly mentioned to be very quiet and thoughtful. Disney's Ariel is energetic, rebellious, anything but demure.
In The Hunchback of Notre Dame, compared to their book counterparts, Quasimodo is much more gentle, Esmeralda is smarter and less naive, and Phoebus is more heroic, with his womanizer tendencies dropped. Meanwhile, Frollo gets Adaptational Villainy and loses all his redeeming traits (which are given to an original character, the Archdeacon of Notre-Dame). In the book Frollo is the Archdeacon, making this a case of the Decomposite Character.
In Tarzan, Kerchak is a stern, but benevolent leader of the apes, rather than the violent, abusive character he is in the books.
Almost everyone in Ultimate Avengers is made much more like their mainstream counterpart, as opposed to their Ultimate version, since those guys are a bunch of assholes.
Iron Man only slightly exhibits signs that he's an alcoholic, drinking one glass when he is fired from the team. Other than that, he's his mainstream counterpart, aside from the part about still supplying weapons. Ultimate Iron Man is so much of an alcoholic that for a few years, you could not see him out of armour and not drinking.
Although still a rampaging monster, the Hulk is drastically tuned down from his Ultimate incarnation, which is literally a psychopathic manifestation of Bruce Banner's Id without any restraints period — Ultimate Hulk is a cannibal, and that's just for starters.
In Mr. Peabody & Sherman, Mr. Peabody's feelings for Sherman are changed from treating the boy as merely his pet and assistant to the dog considering Sherman his dearly beloved son.
Tinkerbell is toned down in Disney Fairies compared to Peter Pan. She isn't clingy and a jerk anymore, instead being a Plucky Girl. She keeps some of her jealous aspects in the books, though.
In the transition from page to screen, many other characters had their personalities changed as well. Most notably, Vidia became rude at worst and outright friendly at best; in the books, she once sold out her race because she was in love with a dragon, stole a wand others risked their lives to get, and was, in general, more of a Jerkass.
A less obvious example is Queen Clarion. Most of her Action Girl characteristics from the books were taken away and given to other characters, her duties were lessened with the addition of the Ministers, and she got a love interest with a tragic backstory, despite never expressing an interest in romance. She was also made much more motherly and removed from the main plot line, when she had previously been a main character.
Miles Morales is more social and assertive than in the comics, where he was shy and an introvert. ItSV also presents Miles's more withdrawn moments as more due to him being transferred from a normal public school to an elite charter school (Brooklyn Visions Academy) and having to dealing with various traumatic events like witnessing with the death of his Peter, discovering that his uncle is a supervillain, and having said uncle soon sacrifice himself to save him. His love of graffiti and hip-hop is also far more emphasized in the film.
Spider-Man: Noir in the comics is a reporter with righteous anger and socialist leanings. This version is a comically serious private eye who's perplexed by any color that isn't in grayscale, leading to his fascination with a simple Rubik's cube.
Peni Parker is presented as a Genki Girl, not the moody teenager of the comics.
In Brian DePalma's version, Norma Watson is made into Chris's gal pal and openly bullies Carrie as well as being in on the prank at the prom. This is due to DePalma being impressed with PJ Soles's performance and rewriting Norma to expand her role.
Again in the TV remake with Tina Blake. While she is one of Chris's friends in the book, she isn't as big a bully and she isn't in on the prank, which she is in the film.
Helen Shyres in the book is mostly just a background character as Sue's friend but gets combined with another girl Frieda Jason in the TV film and so has her scene where she is nice to Carrie at the prom.
Cho in the books was written to be excessively jealous and clingy when she and Harry are dating but none of this is shown in the movies.
The films also made Ginny noticeably more soft-spoken, in contrast to the Fiery Redhead she was in the books.
Narcissa Malfoy also has her Rich Bitch and haughty racism tendencies dropped from the films.
Albus Dumbledore is generally calm and unflappable in the books, which Richard Harris portrayed in the first two films. However, Michael Gambon's performance starting in the third movie due to Harris' death is more emotional and prone to occasional bursts of anger. The main page image illustrates the difference when Dumbledore asks Harry about whether he put his name in the Goblet of Fire; the book mentions that "Dumbledore asked calmly," but in the movie, he accosts Harry and demands to know the truth.
While Bellatrix Lestrange is still psychopathic and sadistic like her book incarnation, she is much more of a Psychopathic Womanchild in the films.
A common complaint among the fandom is the tweaking of Ron and Hermione's characters, since many of the former's shining moments from the books got given to the latter. The end result was a Ron which seemed generally less brave and competent, and a Hermione who comes across as being even more capable and understanding, without the more realistic flaws of the book version.
Professor Snape's Jerkass traits are toned down, and he's more cold and stoic than his violently emotional book counterpart. His love for Lily also comes off as more sympathetic here whereas in the books, its more like he was creepily obsessed with a girl who didnt love him back for thirty years.
Aang is a happy-go-lucky and eager kid in the series. Here he is a quiet, brooding, and somewhat angsty boy.
Sokka, being both the Comic Relief and The Smart Guy in the show, has little in the way of character traits in the film and does little beyond receive exposition.
Admiral Zhao is more confident and violent in the series, while in the film he is more indecisive to the point he often consults the Fire Lord on every decision and he runs away after Iroh makes fire from thin air.
Fire Lord Ozai, the de facto Evil Overlord, is shown as a curious individual in the movie. He doesn't appear as hateful and cruel, but contemplative and decisive. He even shows remorse for his son Zuko's banishment by warning Zhao that Zuko will be over him when he returns. In the show, he's a textbook Abusive Parent to both of his children in very different ways.
Master Pakku. Instead of being a sexist prick, he's just a wise martial arts sensei.
Iroh. In the movie, while he retains his role as mentor to the afflicted Zuko, he is not as comedic and laid-back as his series counterpart.
Zuko is the most similar to the series but he is not as deadset/blind in his chase of the Avatar. He barely lost his temper (a famous character trait for Season 1 Zuko) and actually felt remorse for others, which is shown when he apologizes to an unconscious Katara in the movie, whereas in the series he smugly rubs in his victory over her.
A Series of Unfortunate Events (2004): Count Olaf was written as very sinister in the original books but in the film he is more over the top and hammy leaning closer to comic relief. Granted, it was Jim Carrey who portrayed the character after all.
Jurassic Park: In the original book, Gennaro the lawyer ends up turning into The Lancer for Alan Grant, and he even punches out a Velociraptor! The film turns Gennaro into a Dirty Coward that gets eaten by a T-Rex whilst sitting on a toilet. John Hammond in the original book is The Scrooge and a tyrant who shortchanges people (giving fat programmer Dennis a reason to betray him), has a Never My Fault mentality, and then suffers Karmic Death. The film turns Hammond into a kindly old man who truly thinks that what he's doing is a good idea (which it isn't), and one result of the change is that Dennis comes off as more of a Jerkass for betraying him!
Though, to be fair, Genaro's characterization (and manner of death), mirrors Ed Regis, Ingen's PR guy from the book, making him more of a Composite Character.
Alvin and the Chipmunks, as well as The Chipettes experience this with almost every new incarnation. While the characters have experienced some natural Character Development over the years (especially true of the 1980s cartoon series), they have also experienced complete changes in their personalities when it comes to the later live action/CGI movies. For example, Simon goes from being Deadpan Snarker with biting sarcasm to having a less cerebral sense of humor with a underlying perverted streak; Theodore's innocence and naivete not only becomes a thing of flanderization, but he also becomes more absent-minded (much like Jeanette usually is); and Brittany is hardly the Alpha Bitch diva that she's been known for in previous incarnations.
However, they seem to return to their 80s personalities in the 2015 series.
The Adventures of Milo and Otis: Otis the pug is depicted as a little stuffy and fastidious. In the original Japanese Koneko Monogatari, the narrator says that Otis (known as Puusuke in the original) is somewhat ditzy.
In the books, Annabeth might've been a serious Action Girl, but she was also a Plucky Girl who valued brains more than brawn. The movie focused more on her toughness and made her a lot more abrasive, making her more like Clarisse from the books.
In the comics, both Superman and his adopted father Jonathan Kent are very idealistic and optimistic people, hoping for the best in people. In this universe, Jonathan was pretty paranoid because of Clark's origins as an alien and felt The World Is Not Ready for Clark. As a result of this and constantly being a Hero with Bad Publicity despite his efforts, this version of Clark is also more angsty and brooding about his place in the world. In response to the negative reaction these changes garnered, Superman's personality is significantly realigned in Justice League (2017) in order to bring him more in line with his classic portrayal.
Lex Luthor is very different than the comic version, being portrayed as a sort of Psychopathic Manchild; apparently the idea was to modernize him as an eccentric young tech billionaire, but most fans find him much less threatening than the usually calm, Stoic that he is in most modern adaptations.
Much like in Tim Burton's film, Batman is more open to the idea of lethal force. This version for a time also branded rapists and human traffickers for other criminals to target. However, he begins to undergo Character Development that sees him backing off these more extreme methods and becoming closer to his comic counterpart. Superman's resurrection via the Genesis Chamber and a Mother Box in Justice League (2017) is something Bruce decided, as opposed to his traditional opposition to the use of the Lazarus Pit in the comics.
In the comics, the Barry Allen version of The Flash doesn't have a particularly notable personality, and in fact has a long-standing reputation for being The Generic Guy. The movie version of Barry is the League's Plucky Comic Relief, and is also very neurotic and antisocial to boot.
Captain Kirk of Star Trek: The Original Series is not the same Kirk as the one from rebooted movies. The Continuity Reboot is an Alternate Timeline of the original in which Kirk's father dies seconds after Kirk is born, and his mother remarries a Jerkass; this results in a very different childhood for young Kirk, and thus a different space captain as an adult. Curiously, though, the films portray Kirk as a Flanderization of his original personality; the plot and interactions suggest that the filmmakers weren't trying for this trope, but simply weren't as familiar with the original as they ought to have been. They portray Kirk as The Casanova and a Cowboy Cop, which is what Pop-Cultural Osmosis suggests he was in the original. But in the original, he was described as "a walking stack of books" as a cadet, remained highly respectful of women (even if he wasn't shy about using his charisma), and generally reflected a lot on the moments where he bent the rules to do what was right, earning Starfleet's respect for that (outside of the Obstructive Bureaucrats he annoyed, who would badmouth him in later Star Trek series, exacerbating the Flanderization). In the films, he constantly clashes with authority, gets in trouble by rushing into situations without thinking, and neither Starfleet nor the women he hits on respect him very much (at least at first).
The third film, Star Trek Beyond, depicted him in a manner virtually identical to his TOS characterisation, losing all the less sympathetic and more controversial elements of his earlier reboot portrayal. This could be justified in-canon as him maturing after a couple of years in command of the Enterprise.
Every hero in the universe has been altered to some degree, with the most consistent change being that none of them abide by the Thou Shall Not Kill trope, even the ones who ardently lived by it in the comics.
Many of the characters in Guardians of the Galaxy, since most of them were too obscure for most of the audience to notice or care. Star-Lord goes from a cosmic hero to a sarcastic, jokey outlaw (this becomes Ret-Canon in subsequent comics), Drax becomes extremely Literal-Minded, Yondu goes from being a Noble Savage superhero to a murderous redneck criminal and Anti-Villain, and Ronan the Accuser goes from being a Knight Templar in the Kree military to a fanatical, mass-murdering terrorist who according to Word of God, was inspired by Osama bin Laden.
Helmut Zemo in the comics was, originally, a Neo-Nazi after having been brought up as one by his father, something left out of the film. The character had gone through Character Development in the 2000s to erase this aspect of his character so he could undergo a HeelFace Turn (which unfortunately didn't last), which is where the film seems to draw on, while lacking the non-Nazi-related fascist views he'd develop after returning to villainy. Zemo in the comics also has a penchant for forming teams of superhumans to follow his whims, but in the film he euthanizes the sleeping Winter Soldiers and makes it clear he detests the idea of having more superhumans in the world.
In the Civil War comics, Black Panther was against registration and sided with Captain America on the issue. In the film, because the triggering event of the Accords is the deaths of Wakandaian emissaries and furthered by Cap helping Bucky Barnes, who T'Challa thought killed his father, when really it was the aforementioned Zemo, T'Challa is for registration and assists Iron Man. He's also more hotheaded and impulsive than his comic counterpart (who is usually The Stoic), though he shows signs of moving closer to his classic characterization by the end of the movie.
Princess Shuri is a Gadgeteer Genius and helps design and implement much of the new technology in Wakanda, effectively making her Black Panther's Q. This is a complete 180 from her comic counterpart, who is very spiritual and heavily tied to the mystical aspect of Wakanda. In fact, the comic version of Shuri is probably even more spiritually-inclined than her brother.
T'Challa himself continues this into his own movie. While he is more reserved and serious compared to his fellow superheroes, T'Challa is more emotionally open and forthright in his opinions than his comic counterpart who was very much The Stoic. He is also less smug and condescending than in the comics.
X-Men: Apocalypse changes the already-established characterizations of certain characters from earlier in the series. This was probably a deliberate attempt to show how they'd turn out in the altered timeline created in the previous movie.
Warren Worthington III in X-Men: The Last Stand was presented as a wholesome Nice Guy; in this film, he's an angry and cocky rebel. He later becomes a Horseman of Apocalypse.
Scott Summers is a bad boy instead of a "boy scout" (as he calls himself in the first movie). He encourages a few of his classmates to skip school, and he steals one of Xavier's fancy cars to drive them to the mall.
Kurt Wagner no longer goes hammy to remind everyone that "in the Munich circus, I was known as The Incredible Nightcrawler!", as in X2: X-Men United.
Apocalypse himself only hams it up at certain moments like making a point or being angry, instead being more soft-spoken and calm, whereas Large Ham is his comic counterpart's default setting.
Escape to Witch Mountain: The owner of the orphanage in the movie was a kind lady while in the book, it was more of a home for orphaned juvenile delinquents run by a former police woman who took no guff from anyone.
In The Addams Family films the girl, Wednesday, is usually a scowling Creepy Child and the boy, Pugsley, is usually smiling. In the original panel cartoons it's the other way around.
Asher is consistently happy and cheerful throughout The Giver (where he's assigned a recreational position), while in the film he starts off that way but becomes more serious and unsmiling after being assigned drone pilot.
Bean in the film Ender's Game is made to be a peer of Ender's class, not a younger trainee like he was in the book. As a result he takes on some of book!Alai's traits, including being a bit of a bully to Ender before becoming his friend. This is quite a contrast to Bean's personality in the books, where he wouldn't taunt anybody due to being the smallest student and so preferred to be ignored.
Captain George Stacy was a supporter of Spider-Man from the start in the comics. However, in The Amazing Spider-Man, he starts off distrustful of the webhead and wanting to arrest Spidey before he warms up to him. Additionally, as he's dying, he asks Peter to stay away from Gwen for her own safety, whereas comics!George asked Peter to look after her.
In some ways, Gwen Stacy is the opposite of her comics counterpart, including being accepting of Spider-Man and not blaming Spdiey for her father's death as her classic and Ultimate Marvel counterparts did.
In the graphic novel Watchmen, Silhouette was rather unpleasant and vaguely racist and she was killed after her identity was exposed. In the Watchmen movie, none of those moments are shown.
Hannah Swensen: Moishe and Delores (her cat and mother, in order), can barely interact, even over the telephone... let alone when Delores is there in person. The best that can have expected is Clothing Damage. But in the film adaptations, almost none of this happens.
Who Framed Roger Rabbit massively changed virtually every main character's personality from Who Censored Roger Rabbit? The biggest example of this is Jessica Rabbit who goes from a cold-hearted Femme Fatale who marries Roger only because she was magically compelled to do so by a genie and promptly dumps him for a rich man when the wish expires in the book to a subversion of the Femme Fatale archetype who turns out to genuinely love Roger.
Peter Parker himself is more moody both in-costume and out, generally being less prone to make jokes than the Peter of the comics, and is even an Extreme Doormat out-of-costume, whereas even in the early stories, Peter had a chip on his shoulder and was more confrontational.
In part due to being a Composite Character with some of Peter's other love interests, Mary Jane Watson is more somber and reserved, whereas the comics version was witty and charming, and ease Peter up when he gets too serious.
Billy and Trini are now respectively autistic and questioning her sexuality with the issues that come with those, with Trini additionally being far more snarky; and Zack is a "bad boy" who fears his mother dying from her illness.
Rita lacks many of her series counterpart's more comedic traits.
Jem and the Holograms: The normally straight-laced Aja mentions having gone to juvie for unknown reasons.
In the film version of Middle School: The Worst Year of My Life, the villainous characters get quite some personality changes, as their existing personalities were hard to make work in a kids comedy:
Principal Dwight and Vice Principal Stricker. In the books, Dwight was mainly a background character while Stricker took a more direct antagonistic role. In the film, Dwight is the main villain while Stricker was his right-hand woman. Also, in the book they were both no-nonsense characters, if not the nightmarish caricatures in Rafes imagination, while the film version has them more cocky and bumbling.
Bear, Jules boyfriend in the first book. The book version portrayed a violent and cruel Bear who did nothing but yell at his wife and kids, hence his nickname. In the film, hes portrayed as a narcissistic sleazebag to better fit Rob Riggle.
Miller the Killer was a typical cartoon bully a la Francis in the books. Hes more of a tough-guy rival whose bullying mostly consists of shoving and taunting in the movie.
Clarence Boddicker in RoboCop (1987) took sadistic gleee in his actions. His RoboCop (2014) counterpart Antoine Vallon was more professional and like a businessman in his work (included delegating the task of taking out a pre-RoboCop Alex Murphy to underlings, whereas Boddicker literally delivered the first and final shots to Murphy and watched his men do the rest).
Comic book and cartoon Grouchy in The Smurfs barely speaks except to recite "I hate..." The live-action Smurfs film and its sequel have Grouchy as being very outspoken and opinionated, and sometimes very snarky.