Sudden Name Change

"Bloober swims underwater with its children. It has a relative, the Scattering Bloober, whose children scatter in all directions."

- Description of an enemy, Super Mario Bros 3

"Bloopers love laughing at other Bloopers' bloopers. No one wants to end up on the Blooper reel."

- Description of the exact same enemy, Super Paper Mario

It may be a translator's mistake, a typo, or the author might have had a better idea, but sometimes, a specifically named character or concept introduced in a work of fiction can come to be called by a totally different name later on, often with no explanation at all, or even an implication that their name had always been that. Needless to say, this tends to confuse the audience (sometimes making them think the two names refer to two different things), and authors should try to avoid it.

Super-Trope of Inconsistent Dub (when it refers to characters). Related to Remember the New Guy?.

Anime and Manga

 * In Rave Master a case of Inconsistent Dub occurs in the manga translation. In the first volume or so, Haru's sword is referred to by its Japanese name, the Ten Commandments. Every volume after instead calls it the Ten Powers.
 * Done again when the translator changed, with the Mystic Realm/Makai World and Star/Stellar Memory.
 * In the anime Revolutionary Girl Utena, the main character's last name was incorrectly pronounced "Tenjuu" in the first few episodes, and later corrected to "Tenjou."
 * The first appearance of Celtic Guardian in Yu-Gi-Oh! had him be referred as "Elf Swordsman." Curiously enough, Elf Swordsman was Celtic Guardian's Japanese name.

Comics

 * When Stan Lee forgot The Incredible Hulk's alter-ego is named Bruce Banner and started calling him Bob Banner, it led to a retcon where his full name is "Robert Bruce Banner". He also called Peter Parker Peter Palmer, but at least that was forgotten.
 * In The Incredible Hulk #294 Banner is up against a Corrupt Corporate Executive named Max Stryker. Then Hulk is conscripted into the Secret Wars; when he comes back in issue #295 Stryker is now called Max Hammer.
 * Also in the Marvel Universe, Dr. Druid (who predates The Fantastic Four) was originally called Dr. Droom. When he was reintroduced, his name was changed to avoid confusion with Doctor Doom but no 'in-universe' reason is given for the change.
 * In the Green Lantern comic book series, Carol Ferris's father was originally named Willard, but from his second appearance onward, he was renamed Carl.

Film

 * Brawl from Transformers is for some reason actually referred by the name "Devastator" in the actual movie, but by his real name in the merchandise. The real Devastator actually won't appear until the climax of Revenge of the Fallen.
 * Similarly, Wheeljack and Mirage from Dark of the Moon are actually both referred in-film as "Que" and "Dino", respectively.

Literature

 * Up until Harry Potter finds out the actual name of the creatures that guard Azkaban, a wizarding prison, everyone refers to them as "The Azkaban Guards." After he experience their happiness-draining power and is told their name, Dementors, in Harry Potter and the Prisoner of Azkaban no one refers to them as the Azkaban Guards ever again.
 * Elwe Singollo in The Silmarillion. He's referred to as Elwe in his early chapters, then disappears for a couple thousand years, and then is called Thingol. Because characters in the Silmarillion weren't already hard enough to keep track of. A similar thing happens with Melkor/Morgoth, but there, at least, there's a farily obvious renaming instance.
 * Elwe's example makes sense, because while he was left behind building a kindgdom in Doriath the Elvish language mutated. The Elves in Valinor preserved Quenya, but the new language used by Elwe's subjects was Sindarin, and Thingol is the Sindarin rendering of Singollo.
 * In Dragonflight, the first Dragonriders of Pern novel, the leader of the "old-timers" is T'ton, and Weyrwoman Kylora is Pridith's rider. In subsequent books, the names are T'ron, Kylara and Prideth.
 * Towards the end of the "Wyrmberg" segment of The Colour of Magic, Liessa suddenly becomes Lianna. Given the Pernese influence of the Wyrmberg, it was suggested that this might be an intentional parody of the above, but Terry Pratchett says no, it's a mistake at the printers.
 * In Swallows and Amazons, the little sister of the Walkers is known as "Vicky" the entire first book. The sequels promptly change her name to "Bridget". The explanation given in-story is that baby Bridget looked like "Queen Victoria in old age" and was jokingly nicknamed "Vicky", but the resemblance and the nickname ceased when she grew older. (In real life, author Arthur Ransome was basing several of the characters on real children, and Bridget was the name of their younger sister—when she got old enough to comment on the first book, she disliked the fact that her name had been changed, and Ransome fixed things up for her.)
 * In the Project Gutenberg text of The Haunted Hotel by Wilkie Collins, Lord Montbarry's eldest daughter's name changes from Lucy to Marian between chapters. The same slip is present in the French edition.
 * Brother Bear from The Berenstain Bears actually used to be known as "Small Bear" before his younger sister, Sister was born.
 * In the Warrior Cats series, there are a couple, all due to author error. Owlfeather of WindClan's name mysteriously changes to Owlwhisker. The outcasts in Moonrise introduce themselves by their full names, two of them being "Rock Where Snow Gathers" and "Bird Who Rides The Wind". The full names are only mentioned once; they go by their nicknames "Rock" and "Bird" for the rest of the book. In the next book, their full names have changed to "Rock Beneath Still Water" and "Bird That Sings at Dusk". Bird appeared again in later books, and the authors attempted to fix their mistake; she is now "Bird That Rides The Wind".

Live Action TV

 * In the Psychiatrist Milkman sketch on Monty Python's Flying Circus, Mrs Ratbag's name changes to Mrs Pim with no notice. Which is to say, in the beginning of the sketch she's called Mrs Ratbag and later on she's called Mrs Pim, but it's the same character.
 * The Price Is Right: A pricing game known as "Now and Then" (where one must guess whether the prices of grocery items are their current price or one from an old supermarket flyer, the titular "now" and "then" prices) had its title changed to "Now or Then", for almost no apparent reason.
 * The Greatest American Hero's secret identity was initially "Ralph Hinkley," but then after a guy named Hinkley tried to shoot the president in real life, he was referred to as either "Ralph" or "Mr. H" and the nameplate on his office was shown as "Ralph Hanley."
 * On Boy Meets World, Topanga states that her mother's name is Chloe in season one but in a later season her mother's name is Rhiannon.
 * Are You Being Served: in one episode it's revealed that Mr. Lucas' first name is Dick. In other episodes where it comes up, it's James.
 * Two female monsters from Sesame Street actually suffered from this. A female pink monster who was originally named Mooba was inexplicably renamed Google, and a female green monster who was originally named Google was inexplicably renamed Phoebe.
 * Happened on CSI: NY, one of the recurring detectives was Jessica Angell at one point and Jennifer Angell at another.

Pro Wrestling

 * Although name changes in Professional Wrestling occur often due to gimmick changes, sometimes names are changed for no apparent reason. Case in point, John Hennigan officially debuted on WWE Raw as Johnny Blaze, but was changed to Johnny Spade the very next week with no gimmick change. It would become Johnny Nitro just a few weeks later, but this name would eventually get a change in gimmick.
 * The Blaze-to-Spade change could've been because of Marvel Comics having a well-known Ghost Rider by the name Johnny Blaze.

Radio

 * In the Marx Brothers' radio show Beagle, Shyster and Beagle Waldorf T. Beagle's name was changed to Waldorf T. Flywheel (and the show renamed Flywheel, Shyster, and Flywheel) because a real lawyer named Beagle threatened to sue. In-Universe it was explained that Flywheel had gotten divorced and went back to his original name.

Theatre

 * Invoked in a Monty Python stage sketch in which there's a bartender who's called (and answers to) different names by all of his customers.

Video Games

 * The squid Mook from Super Mario Bros. was originally called "Bloober". Starting in Paper Mario, its name was changed to "Blooper".
 * Princess Peach had been called Princess Toadstool in America, until Super Mario 64, wherein she was given her original Japanese name. The name "Princess Toadstool" still pops up now and then, though, so people tend to assume that Peach is her first name, Toadstool her surname.
 * A Nintendo How-to-Draw book had Bowser referred as "Kerog."
 * Doubly weird is the popular fan theory that because of one of his sons' names, Bowser's actual name must be  No wonder he goes by "Bowser".
 * Warcraft III introduced Furion Stormrage to lore. The expansion pack arrives a year later and his given name is expanded to Malfurion with no explanation.
 * In addition to the Furion / Malfurion example, Owlbears are renamed Wildkin, while Ballistae, Catapults, Steam Tanks and Gyrocopters become Glaive Throwers, Demolishers, Siege Engines and Flying Machines respectively, with completely new models and attacks. Why exactly is never mentioned.
 * In the Final Fantasy series, the change from Aeris to Aerith. Although, in this case, there had always been an inconsistency; starting in Kingdom Hearts, they finally settled on the latter.
 * The difficulty arising from the fact that the Japanese name "エアリス" ("EH-AH-RI-SU") could be properly translated to either "Aeris" or "Aerith."
 * Doctor Eggman, the Big Bad of the Sonic the Hedgehog series games is always referred as "Doctor Robotnik" in the US version of earlier games. However, later games changed this so he is now always referred as "Eggman." But then this was changed again so that Eggman's real name is actually indeed Robotnik, but everyone still calls him Eggman anyway.
 * A character in Jak and Daxter The Precursor Legacy is referred to as Jak's uncle, but in all later released material is instead known as the explorer.
 * Erol's name from Jak II changed to Errol in Jak 3. A Fanon explanation is that the extra r refers to.

Web Original

 * Anna, one of the main characters in The Rapture Logs, was named Jane until about halfway through Act III, when "creative difficulties" with the person on whom the character was based necessitated the name change, which was applied retroactively through the archives.
 * Sailor Moon Abridged has fun with the Silver Imperial Moon crystal, which is never called the same way twice, even by the people looking for it.

Western Animation

 * Three from Code Lyoko:
 * Due to a translation mix-up, the supercomputer was originally called the "supercalculator" in the English dub. This was later corrected.
 * The fictional band The Subsonics was changed to The Subdigitals when it turned out there was a real band called The Subsonics.
 * Kankrelats were called "Roachsters" in the first season. They were latter given their original French name.
 * A strange example: The earlier Looney Tunes cartoons featured a character called Egghead, occasionally portrayed as a recreational hunter. In one cartoon, his name, for no reason at all, was changed to "Elmer Fudd". Through the years, the character changed radically, becoming the stuttering, bald, bumbling hunter we recognize today, known exclusively as Elmer Fudd—one character become another by way of an altered name.
 * In Avatar: The Last Airbender, Flying Bison are later referred to as Sky Bison. It could be possible that both terms are correct, though, since many animals have multiple common names.
 * Considering they are also referred to as Wind Buffalo by a Fire Nation tourist, that seems likely.
 * The New Adventures of Superman. In several early episodes (e.g. "The Deadly Dish") Lex Luthor's henchman was named Blinky. In the first Season 3 episode "Luthor's Lethal Laser" the henchman's name was changed to Kinky, with no explanation.
 * Is the featherduster's name Fifi or Babette?
 * Shockwave from Transformers Animated was actually given the name "Chugway" in the subtitles for the episode "Autoboot Camp."
 * The Coachman from Pinocchio was actually referred as "Barker" in the film's subtitles when he finally brings several boys which he kidnapped (including Pinocchio himself) to Pleasure Island. However, the subtitles start to refer him as "Coachman" again when he and some gorilla-demon-looking-things start to round the now-transformed boys into crates headed for either the salt mines or the circus.
 * A minor villain from Cars 2 whose first name appears to be Fred actually alternates between the surnames "Fisbowski" and "Pacer."
 * Similarly, Sal Machiani (a yellow three-wheeled truck seen in Italy) is actually referred as "Ape" in one of the film's promotional posters.
 * Yet another minor villain, Petrov, actually alternates between the surnames "Trunkov" and "Oilski."
 * Daisy Duck was actually referred as "Donna Duck" in her debut short, Don Donald. It wasn't until her second short in which she was beginning to be referred to as her current name.
 * And Goofy used to be known as "Dippy Dawg."
 * Mei Li, the pig princess from one episode of the Kung Fu Panda animated television spinoff was actually known as "Pei Pei" in some promotional media.

Real Life

 * A great many streets and highways will change their name as you drive down them for no apparent reason. This can be very confusing and cause you to get lost. The reason tends to be things like it used to be two streets that were combined or you crossed a state or county line.
 * This very wiki does it with changing names of trope pages all the time.