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* Amy Lawrence only receives a brief mention in Literature/TheAdventuresOfTomSawyer, when Tom accidentally reveals to Becky that he was "engaged" to her before Becky. In ''WesternAnimation/TomSawyer2000'', she's a supporting character who still feels UnrequitedLove for Tom, [[spoiler: and eventually ends up with Huck]].
* In ''Akata Warrior'', the sequel to ''Literature/AkataWitch'', Sunny's brother Chukwu is much more important to the plot than in the first book and in fact sets off much of the main plot.
* Emily Bennett in the ''Literature/{{American Girl|sCollection}}'' books originally appeared in ''one'' book, for two weeks of a story (the Molly franchise) that details almost a year and a half. Since she got her own doll, she's been retconned into more of the story. TheFilmOfTheBook does it even more.
* ''Literature/{{Animorphs}}'':
** Erek was introduced in #10 as a one-off character, named after a fan who won a contest. However, he had the perfect skill set to spy on the Yeerks and was also established as knowing that Marco's mother was Visser One's host, making him an easy catalyst for reintroducing her in #15, his second appearance. By #20, Marco (who narrated #10, #15, and #20) considers his dropping in with information more or less routine, and Marco's ''next'' book, #25, establishes the plot-enabling concept of having Erek and his friends impersonate the Animorphs so that their families won't miss them if they have to go on longer missions. The very next book, narrated by Jake, has Erek act as a GuestStarPartyMember and the book after ''that'', focuses on rescuing him. He was created as a Character of the Day, but he ends up being so convenient and helpful to both the author and the characters that he was, in the end, probably the most influential of the side characters, facilitating and enabling numerous plots throughout the series and playing a huge role in the final battle.
** For most of the series, Tom is a background villain, only having any starring roles in two books (''The Capture'' and ''The Conspiracy''). Come the final five books, he takes Taylor's role as TheDragon to Visser Three and even eclipses him in threat level to the kids, being a much more proactive character than the Visser by that time.
* In ''Literature/TheArtOfArrowCutting'', the main character is Michaelangelo "Mage" Magistrale. The sequel, ''Shadows Bite'', follows Takumo and Kelly Barbet, and Mage is a minor character.
* Mallory in ''Literature/TheBabySittersClub'', who started out as a baby-sitting charge.
* ''A Biography of Tadeo Isidoro Cruz'' by Creator/JorgeLuisBorges is about a secondary character from the epic poem ''Martin Fierro''.
* ''Literature/TheBlackCompany'', first book of the series of the same name, includes The Ten Who Were Taken, ten ancient wizards of great power. By the end of the book, it appears that all ten have been killed, but some survive in secret to reappear later in the plot. Two of these survivors had no speaking lines in the original book, and one of them was never even seen by the narrator, requiring one of the Company Brothers to shout out her name upon discovering her so the reader can realize what's happening.
* ''Franchise/BuffyTheVampireSlayer'': Victor and Jason are two of the several interchangeable {{Mook}}s from the first two episodes who ran away after Luke died. In ''Portal Through Time'', Victor is a major [=POV=] character and the biggest threat to the Scooby Gang in the book, and Jason has a few important scenes.
* Some theatrical and film adaptations of ''Literature/AChristmasCarol'' do this with minor or unnamed characters, such as Mrs. Dilber in the 1951 film, and the third Cratchit daughter (given the name Kathy) in the 1970 musical film. Scrooge's ex-fiancee Belle (or whatever she is renamed) usually gets a larger part in the Christmas Past sequence, in at least one version she is even shown in the present, and the 1970 film made her one of Fezziwig's daughters. The 1951 film also includes a heartwrenching scene of Fan's DeathByChildbirth. Tiny Tim usually also gets more screen/stage time.
* Bosie in ''Literature/ColdMountain'' was barely described in the book. He's arguably the most entertaining thing about the movie, becoming a sardonic, acrobatic, sharp-shooting albino prone to nosebleeds.
* [[FriendlyNeighborhoodVampire Fred]] and [[AlphaBitch Cathy]] from Literature/TheCornersvilleTraceMythos make their first appearances in ''I Kissed a Zombie, and I Liked It'' as side characters, but are vital to the plot in ''Extraordinary*''
* Literature/{{Discworld}} has numerous {{Ascended Extra}}s, from Detritus, who started out as a Splatter (like a Bouncer, but he used more force) who didn't even get a line in ''Literature/GuardsGuards!'' and eventually worked his way up to being a Sergeant in the City Watch, to Ponder Stibbons, who started out as an inconsequential student at Unseen University and managed to become a senior faculty and later the Archchancellor's right hand man (and by virtue of being the only one of this select group that ever does any actual work, de facto ruler of the University).
** Igor is definitely this, starting as a generic gag as part of the whole Hammer Horror/Transylvania/Uberwald schtick and developing by stages into a whole race or clan of meta-humans with all SORTS of medical and scientific abilities, Igorinas, etc
** But Discworld's best example is probably DEATH. He first showed up in ''Literature/TheColourOfMagic'' as a one-off gag, and has since become one of the most major characters in the series, with at least a cameo in every book but one and several stories that star him. Later on, the same happened for the Death of Rats, as it went from a one-off joke to a steady sidekick to Death, with some non-minor roles in most of Death's books.
** Terry Pratchett declared that Sam Vimes was planned to be a support character for Carrot, but it just so happened that the whole Watch series ended up revolving around Vimes instead.
*** Unlike most examples, this came more about because of Carrot's character development rather than Vimes. After his first appearance, one of Carrot's major traits is that it is ambiguous whether he is really a naive, simple person that believes everyone has some good within them or if he is essentially manipulating everyone with this persona. The ambiguity wouldn't work if it was from Carrot's perspective.
*** The entire Watch as written in ''Guards! Guards!'' was intended as a one-off ADayInTheLimelight / TakeThat to other writers that would relegate them to secondary status. Like Death, though, the Watch proved to be so popular with readers that they became the trope, spawning their own arc of stories. "I wanted to give them a day in the sun, but it turned out to be a full-blown tropical holiday."
** The Librarian entered the series as a one-shot gag about one of the many changes the Octavo's spell made in ''Literature/TheLightFantastic''. He's gone on to make appearances in almost as many books as Death.
** Because of the nature of the ''Discworld'' series, characters tends to zigzag in and out of extra/main character. There is no overall narrative, but many different storylines taking place within the same world. So characters like Angua and Carrot will be main characters if the book in question is from the "Watch" subset, but also feature as cameos in non-Watch books. A good example of this sort of thing is Cut-Me-Own-Throat Dibbler, who served as a recurring-gag-cameo in several books before ascending to major character status in ''Literature/SoulMusic'' and ''Literature/MovingPictures''. Then he went back to extra status. Then ''Literature/TheTruth'' had him featuring prominently again. Whether a character is appearing in a starring role or as a backround person all depends on where Pratchett is swinging the metaphorical spotlight during that book.
** Perhaps part of the reason for the trope happening often in Discworld is the high degree of CharacterDevelopment that occurs, particularly when a contemporary character gets plenty of attention. That's what happened to Vimes—he developed from a dejected KnightInSourArmor to a justice-minded GenreSavvy CowboyCop. Death's development was even more dramatic. He started out an emotionless AnthropomorphicPersonification but by the time of ''Reaper Man'' we see the modern Death of Discworld; he sees his job as SeriousBusiness: the reaper who harvests the old lives to make room for new lives and does what he does so as to maintain order; in so doing, he heels he must also protect his charges from outside influence like the Auditors.
** In ''Literature/LordsAndLadies'', Agnes/Perdita is just one member of Lucy/Diamanda's teenage coven, albeit the most sensible and a viewpoint character for one scene. In ''Literature/{{Maskerade}}'' she's the viewpoint character for about half the book, and Perdita has gone from being the "witchy" name that all Diamanda's group have to a SplitPersonality.
** ''Literature/TheAmazingMauriceAndHisEducatedRodents'' were first mentioned in ''Literature/ReaperMan'' as a quick gag where Literature/ThePiedPiperOfHamelin is reimagined as a con artist. After that... well, considering there's a work page for a book where they are the eponymous characters...
* ''Franchise/DoctorWhoExpandedUniverse'': The short story "She Won't Be Home" in ''Short Trips: The History of Christmas'' is from the point of view of a woman named Linda Grainger who encounters the Doctor, and features a ''very'' brief reference to her having a "Grandad Edward". The collection ''Short Trips: The Centenarian'' is ''entirely'' about Edward Grainger, and how his life became inextricably linked to the Doctor.
* Put to extensive use in the ''{{Literature/Doom}}'' series. The cover to the [[{{VideoGame/Doom}} first game]] featured a second marine running toward Doomguy in the foreground. He was given a GenderFlip and a personality and made into the {{Deuteragonist}}, Arlene Sanders. Arlene is Fly's best friend and partner through hundreds of monsters, the moons of Mars, "hell", and the galaxy. But they're [[TheNotLoveInterest only buddies]].
* In the ''Literature/DreambloodDuology'', Mni-inh, Wanahomen, and Hendet -- minor side characters in ''The Killing Moon'' -- become point of view characters in ''The Shadowed Sun''.
* ''Literature/{{Dune}}'': Duncan Idaho has a minor (if significant) part in the first book. He returns in ''Literature/DuneMessiah'' [[spoiler:despite having died in the first book]] for a slightly more major part, and by the [[Literature/ChapterhouseDune end of the series]], he's practically the only true constant in the Universe. [[spoiler:He's been cloned and killed so often that the afterlife probably has a "Duncan Idaho" section.]] He is the only character to appear in every novel, excepting only the novels that take place before his birth.
* Zalasta of ''Literature/TheElenium'' is introduced in a quick scene where he is established as an old friend of Sephrenia's. In ''Literature/TheTamuli'' he plays a much larger role as an advisor to the protagonists and in the end [[spoiler:he is revealed to be the BigBad behind everything that has happened in Eosia for the last 500 years.]]
* It’s common in ''Literature/TheExpanse'' series for a minor character in one book to become a major POV character a couple of books later.
** Dmitri Havelock is briefly Miller’s partner in ''Literature/LeviathanWakes'' and comes back in ''Literature/CibolaBurn'' as a POV character and main view into the antagonist’s side.
** Basia Merton makes a couple of appearances in ''[[Literature/CalibansWar Caliban's War]]'' as one of Prax’s friends who also has an immunocompromised child and also comes back in ''Literature/CibolaBurn'' as a POV character one of the first settlers on the new planet.
** Michio Pa is the enigmatic first officer pulled into the various conspiracies of ‘''[[Literature/AbaddonsGate Abbadon's Gate]]’’, but isn't fleshed out character in her own right until she becomes the pirate queen and one of the main POV characters in ''[[Literature/BabylonsAshes Babylon's Ashes]]'’ .
** Camina Drummer is introduced as chief of security and trusted associate of Fred Johnson in ''Literature/NemesisGames'', but the reader doesn’t really get to know her until she becomes the head of the Transport Union and major POV in ’'Literature/PersepolisRising’'.
*** This only applies to Drummer in the books - in the [[Series/TheExpanse TV series]] she’s a major character from the start due to being a [[CompositeCharacter composite]] of four different characters, including book - Michio Pa.
** Colonel Aliana Tanaka has a minor role as a MoreSeniorSubordinate to Santiago Singh [[spoiler: the Laconian governor of the conquered Medina Station]] in ’'Literature/PersepolisRising'' . However, by ''Literature/LeviathanFalls'', she’s the main villain POV and acting at cross purposes to the crew of the Rocinante.
* The first book of ''Literature/TheFindersStoneTrilogy'' introduces Giogioni Wyvernspur, a PluckyComicRelief side character whose misadventures don't really have any bearing on the main plot. The second book makes him one of its main characters.
* [[MauveShirt Jo Shanks]] doesn't do much in ''Literature/TheGreenEmber'' series, short of being another soldier who has more lines compared to various other background characters. In ''The Last Archer'', he's the main character, and almost all of the story is told from his POV.
* Neville Longbottom in the ''Literature/HarryPotter'' books was a fairly minor character until book 5 when he TookALevelInBadass and became much more prominent.
** Zigzagged with Ginny Weasley. In the [[Literature/HarryPotterAndThePhilosophersStone first book]] she only had one brief appearance, but in the [[Literature/HarryPotterAndTheChamberOfSecrets second book]] was essential to the plot. She then fell OutOfFocus until the [[Literature/HarryPotterAndTheOrderOfThePhoenix fifth book]]. And then in the [[Literature/HarryPotterAndTheDeathlyHallows final book]], she had a minor (but important) role again, due to the Golden Trio being busy on their mission.
* ''Literature/TheHeroesOfOlympus'':
** "D-list goddess" Khione plays a major role. Gleeson Hedge (referenced once in TLO) is another example. Will Solace and Jake Mason may also apply.
** Hylla, Circe's assistant, last seen in ''Sea of Monsters'' turns up again as Reyna's sister and queen of the Amazons.
** Reyna and Nico di Angelo ''multiple'' times -- at first Reyna appears in ''Literature/PercyJacksonAndTheOlympians'' as one of Circe's assistants, and when Jason remembers details of Camp Jupiter, makes special mention to remember ''her''. Come ''Son of Neptune'', Reyna becomes a major supporting character. Nico, a major recurring character in ''Olympians'' returns as a supporting character throughout the series. In the conclusion, ''Blood of Olympus'', both Reyna ''and'' Nico are viewpoint characters, the only two narrators who are not one of the seven.
* According to the foreword to the omnibus edition of the books, Marvin from ''Literature/TheHitchhikersGuideToTheGalaxyTrilogy'' was intended as a one-scene joke in [[Radio/TheHitchhikersGuideToTheGalaxy1978 the original radio play]] until series producer Geoffrey Perkins talked Adams into developing him further.
* Several Havenite characters in the [[Literature/HonorHarrington Honorverse]], with Thomas Theisman the most notable. In ''The Honor of the Queen'', he's a minor, almost forgettable destroyer skipper who appears for a handful of scenes. By ''Ashes of Victory'', he's a linchpin of the series and a major POV character in his own right. Who would have guessed back in his first appearance that he'd change the entire course of the series?
** Anton and Helen Zilwicki (Jr.) were throwaway characters who appeared in one page in The Short Victorious War, when they are on a freighter-transport in a convoy attacked by the Havenites. Captain Helen Zilwicki (Sr.) commands the escorts and gives the Havenites a Pyrrhic victory. Anton goes on to become an intelligence agent/cowboy diplomat in one of the spin-off series. Helen Jr. becomes a main character in the other spin-off series.
* ''Literature/WarriorCats'':
** Several minor characters ended up getting their own side stories, such as Sasha in ''The New Prophecy''.
** Nightcloud was a minor character in [[Literature/WarriorCatsTheNewProphecy The New Prophecy]], the second [[MythArc arc]]. In the [[Literature/WarriorCatsPowerOfThree third arc]], she becomes Crowfeather's mate and one of the more prominent [=WindClan=] characters.
** Rosetail was an elder in the first book, ''Into the Wild'', with such a minor appearance that she didn't even appear in the character list in the book. Fans picked up on that and so in ''Bluestar's Prophecy'' the authors made her one of Bluestar's closest friends growing up.
** Rowanclaw was another minor character, barely mentioned outside the character list -- so minor that he changed from a she-cat to a tom by accident. The authors decided to acknowledge this by making him Tawnypelt's mate, and he eventually went on to become [=ShadowClan=]'s leader.
** Sunbeam was originally a background character so minor that she only appeared in two of the first ten books she was alive for, saying only ''one word'' onscreen. To the readers' surprise, she was chosen to become a protagonist in the eighth arc, ''A Starless Clan''.
* In Creator/HarryTurtledove's ''Literature/HowFewRemain'', Prussian diplomatic attache Schifflen nearly runs down a careless little girl who charges into the street in front of his horse. In the later Great War and American Empire series, that little girl is one of the primary viewpoint characters.
* Max the Dog in the animated version of ''WesternAnimation/HowTheGrinchStoleChristmas'', and Cindy Lou Who in [[Film/HowTheGrinchStoleChristmas the live-action film]].
* ''Literature/TheHungerGames'' has a few examples.
** Katniss's inner monologue mentions former District 7 tribute Johanna Mason while contemplating strategies. In the second and third books, Johanna is a major character.
** Delly Cartwright gets a very mild case, getting name dropped in the first book when Peeta needs to come up with something to bail out Katniss with. In Mockingjay, Delly shows up for a stage of Peeta's treatment.
** In the first book Plutarch wasn't even named, he was just the gamemaker who was shocked and lost his balance when Katniss shot at their dinner.
* Creator/PhilipPullman's novel ''I Was a Rat'' basically looks at what happened to Literature/{{Cinderella}}'s page-boy when he was never returned to his rat state after the ball and has to make a life for himself as a human.
* In ''Literature/JamesAndTheGiantPeach'', the rhinoceros that kills James' parents is only mentioned at the very beginning in the book. The 1996 [[TheFilmOfTheBook film of the book]], however, gave it a ''severe'' upgrade into a major antagonist: it's more of a demonic, lightning-spewing manifestation of James' fears than an actual rhino.
* ''Literature/JeevesAndWooster'': [[TheJeeves Jeeves himself]]. In "Extricating Young Gussie", the first story featuring Bertie, Jeeves was merely mentioned in passing a few times as Bertie's valet. According to WordOfGod, he'd never been intended for a larger role than that, and only became the character we know today in the second story, "Leave It to Jeeves" (later edited and republished as "The Artistic Career of Corky").
* In Creator/LarryNiven's ''Literature/KnownSpace'' series, the Hindmost is a very interesting variation on this trope. In the original ''Literature/{{Ringworld}}'' novel, he's mentioned in passing, but shows up in the next three sequels (''The Ringworld Engineers'', ''The Ringworld Throne'', and ''Ringworld'sChildren'') as a supporting character. He's a bit of a flat character, however, and we never learn his real name or much of his past history other than he used to rule the Puppeteers. The latter-written prequels ''Fleet of Worlds'', ''Juggler of Worlds'', ''Destroyer of Worlds'', and ''Fate of Worlds'', feature as a primary character a Puppeteer scientist named "Baedeker" who later becomes Hindmost of the Puppeteers. The same Hindmost, in fact, who appears in the ''Ringworld'' novels.
* In ''Literature/TheHobbit'' Gollum is originally a minor character who has a courteous parting with Bilbo leaving the cave even taking the One Ring with him. However his role was greatly expanded in ''Literature/TheLordOfTheRings'', so much so that Tolkien had to go back and rewrite the chapter so Gollum and Bilbo part on far more hostile terms.
** Arwen barely appears in the story proper to ''Literature/TheLordOfTheRings'', but she has a major role in the {{Backstory}}. [[Film/TheLordOfTheRings The films]] used material from the appendices, which explained her role, to make her a prominent player in the three films.
** Gothmog in ''[[Film/TheLordOfTheRingsTheReturnOfTheKing The Return of the King]].'' One mention in the novel (it's never even specified what race he is) becomes a memorable turn in the film with Gothmog as a severely deformed but competent orc general.
* ''WesternAnimation/MeetTheRobinsons'' is also adapted from a children's picture book, but oddly, only really does this for Mr. and Mrs. Robinson and Louis. In the book, the former two were rather flat characters with little relevance to the strange goings-on the book focused on... and Louis was an extreme example of the FirstPersonPeripheralNarrator, being a first-person narrator lacking even a ''name''. Most of the other characters are only minorly expanded, or new to this version.
* ''Literature/AMemoryOfFlames'':
** Vale goes from being the nameless leader of the Adamantine Guard in ''The Adamantine Palace'' to a heroic protagonist in the next two books.
** In ''Order Of The Scales'' the nameless Adamantine Guardsmen that tries to kill [[spoiler:Silence]] is fully fleshed out in ''The Black Mausoleum''.
* Grady Hendrix' ''Literature/PaperbacksFromHell''. It's noted in Chapter 8 that Franchise/HannibalLecter was a minor character in Thomas Harris' ''Literature/RedDragon'' who became a major character in the sequel ''Literature/TheSilenceOfTheLambs''.
* ''Literature/PercyJacksonAndTheOlympians'' series has Silena Bauregard who didn't even speak in the first three books, and only says one line in the fourth suddenly catapults into being a significant and important character in Book 5, the last book before the spin offs.
** Same could be said of Charles Beckendorf, though his significance only comes around [[spoiler: after his death.]]
* The cricket from ''WesternAnimation/{{Pinocchio}}'': in [[Literature/TheAdventuresOfPinocchio the original story]], he was a nameless cricket who was squashed by the title character early on and appeared later as a ghost. In the [[Franchise/DisneyAnimatedCanon Disney version]], he was given the name Jiminy Cricket and promoted to CharacterNarrator. Not only did he practically steal the movie away from its title character, but he's gone on to host/narrate other Disney films, short subjects, and even theme park shows. He's also a notable character in several of the ''Franchise/KingdomHearts'' games.
** Not just the Disney adaptation, though the Disney adaptation surely is the cause. Almost every adaptation will give the cricket (or an equivilent bug) an unreasonably huge role. One way of how telling this is is that one movie took out the Blue Fairy (who didn't give him life in the original but was still a mother figure and was more of a conscience-guide than the cricket) but still kept the cricket character.
* ''Literature/TheRealmOfAlbion'' tells the story of Penarddun, a character mentioned just once in ''Literature/{{Mabinogion}}''.
* ''Literature/{{Sandokan}}'': James Brooke, the historical first White Rajah of Sarawak, was a minor character in the novels, being only mentioned in ''The Tigers of Mompracem'' as a fierce enemy of the pirates and in Guillonk's backstory, the villain in the second half of ''The Pirates of Malaysia'' (and would have been dealt swiftly if lord Guillonk didn't happen to visit right as Yanez was making a fool of him), and a mention in ''The King of the Sea'' as the uncle of the new White Rajah. The various animated series and live action series and movies make him Sandokan's main adversary.
* Irene Adler is frequently PromotedToLoveInterest or upgraded to a major supporting character in non-{{canon}} Literature/SherlockHolmes works, even though she only appeared in one original Doyle story ("A Scandal in Bohemia"), and Holmes only briefly encountered her in said story. She makes an impression on Holmes in her brief appearance (understandable, since she's one of the only people ever to outsmart him), but her actual role in the {{canon}} series is minimal.
** This actually goes for most of the characters people think of as the major cast of the Sherlock Holmes stories. Only Holmes and Watson appear in every story (or nearly every story in Watson's case). Lestrade has only a scant handful of appearances, only slightly more than other police officer characters. Mrs. Hudson is an almost invisible presence (Doyle has her as Mrs. Tuner on one occasion, though this is a writer who had Watson forget his own name). Moriarty appears for the first time in the same story he dies in (then once or twice retrospectively). Mycroft only appears once or twice and doesn't do much. Mary Morstan is pretty much a non-presence after The Sign Of Four. In adaptations these roles are almost always vastly expanded and/or heavily recurring.
* ''Every character'' in the film ''WesternAnimation/Shrek1'' that wasn't made up for that adaptation is an Ascended Extra, given that it was originally a [[Literature/{{Shrek}} picture book]]. This includes Shrek himself, the dragon, Donkey, Lord Farquaad (from the Knight -- their specific roles are different, but the parallels are obvious), and Fiona (from the Ugly Princess).
* In the ''{{Literature/Slingshot}}'' series, [[spoiler: Elaine]] starts out as a side character or potential future antagonist. [[spoiler: SAM's attempt at rescuing Jake, her abduction by the protagonists and learning Patrick's death put a nail in that and she becomes a very useful member of the main group of protagonists.]] Something similar happens with [[spoiler: Major Yonas, who starts out hunting the main characters for a shadowy government agency, but near the end gives up on that job and helps the main characters to escape.]]
* In ''Literature/SpellsSwordsAndStealth'', four {{Non Player Character}}s from a ''TabletopGame/DungeonsAndDragons'' {{Expy}} tabletop game suddenly find themselves at the center of an incredible adventure when four [[PlayerCharacter adventurers]] get themselves killed in a stupid manner in a local tavern because the players didn't bother reading the rules or listen to the GM. The [=NPCs=], a town guard, the daughter of the town mayor, a gnome with a shady past, and a half-orc bartender, find a scroll that appears to be the summons from the kingdom's [[TheCaligula mad ruler]], who is known to raze entire towns to the ground for any real or perceived slight. They're faced with a choice: if they do nothing, the king is likely to wonder why the adventurers never showed up at his castle and send out a search party which would, eventually, result in the deaths of everyone they know and love. Alternatively, they can hide the bodies and assume the identities of the four adventurers and hope to die far away from their home town to spare their loved ones. In a strange twist of fate, [[spoiler:this ends up helping them, when all "real" adventurers find themselves constantly rolling {{Critical Failure}}s in the dungeon thanks to a RealityWarper artifact that affects not only the "game" world but also RealLife. Additionally, the group also meets three other would-be adventurers who may have found themselves in the same predicament]].
* ''Literature/DarthBane'': Johun started off as a name in a sourcebook for the Dark Forces Saga. In ''Rule of Two'', he's one of the main characters.
* In ''Literature/TimeRiders'', Ronald Waldstein was originally only referred to in conversations, then eventually became a major character.
* Lydia had one notable scene in ''Literature/TrappedOnDraconica'' but after a TimeSkip she's one of the main heroes in ''Literature/LegacyOfTheDragokin''. She gets as much screen time as [[TheHero Daniar]].
* In ''Literature/TheTwilightSaga'', Jake Black ascends from a SmallRoleBigImpact in the first book to a {{Tritagonist}} in the later books, and arguably a Deuteragonist in the second. Sam, who has exactly 2 lines in a single conversation in the first book, also becomes a more major role in the later books.
* Sydney Sage, who played a supporting role in the last two books of ''Literature/VampireAcademy'', became the main character in the entire series of ''Literature/Bloodlines''.
* In ''Literature/WelcomeToNightVale'', protagonist duties are shared by Diane Crayton, whose biggest role in the ''Podcast/WelcomeToNightVale'' podcast was a speaking role in "The Debate" episode, and Jackie Fiero, who had one line in one segment of Episode 55.
* Creator/KurtVonnegut does this to several secondary characters in his early novels. For instance, AuthorAvatar Kilgore Trout appears as a minor character in Literature/SlaughterhouseFive, and is one of the two principal protagonists in Vonnegut's later novel Literature/BreakfastOfChampions.
* In ''Literature/TheWellOfMoments'', Jasmine Treager takes the lead role after having only a limited part in ''Literature/TheAffix''. Many of the other major characters were bit players in the first book too.
* Tigger was a minor character in the original ''Literature/WinnieThePooh'' novels by A.A. Milne, only appearing in ''The House At Pooh Corner''. In the Disney {{Animated Adaptation}}s, his role was expanded, making him the most prominent character after Pooh himself (and perhaps even topping him!). Roo seems to be undergoing a similar evolution in more modern features (though it is probably worth noting nearly every character has gained a plausible amount of screen time at some point, due to the Disney interpretation's tendency to give ADayInTheLimelight).
* In the ''Literature/WolvesOfMercyFallsSeries'', Isabel and Cole went from being supporting protagonists to getting an entire book focusing on them.
* In ''Literature/TheWonderfulWizardOfOz'', Boq is an extremely minor character -- a rich Munchkin who lets Dorothy stay the night at his house before she leaves Munchkinland. In ''Literature/{{Wicked}}'', Boq is a decently significant supporting character during the Shiz University portion, even narrating an entire chapter. Better yet, in [[Theatre/{{Wicked}} the musical]], he [[CompositeCharacter becomes the Tin Man]].
** The Good Witch of the North is a relatively minor character in the books, as opposed to Glinda, the Witch of the South. In Volkov's version, where she is called Villina, she is the more prominent one. Added to that, the 1939 movie turns the two into a single CompositeCharacter, Glinda the Good Witch of the North, who performs the roles taken on by both characters in the book. This also became a case of AdaptationDisplacement, as virtually every ''Wizard of Oz'' adaptation made after the 1939 film stuck with the character composite (even the ''Literature/{{Wicked}}'' novel, which was in many ways more faithful to the L. Frank Baum novel than to the film version).
* Creator/StephenKing's Holly Gibney, a talented, autistic-coded protegee to ''Literature/MrMercedes'' protagonist Bill Hodges and later a private investigator in her own right, was originally supposed to just appear in a single scene in the aforementioned novel. She became part of a trio of protagonists with Hodges and Jerome Robinson that remained throughout the trilogy, became deuteragonist of ''Literature/TheOutsider2018'' and protagonist of the short story ''Literature/IfItBleeds'' and then had her first full length solo adventure ''Literature/{{Holly}}''.

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