OC Stand-In

A subtrope of Original Character. An OC Stand-In is a canon Flat Character that gets little screentime or few (if any) lines, and therefore can be molded into whoever the fans want. Often, they may not even have canonical names. Thus an OC Stand-In is like an OC, but the fact that these characters usually have at least some personality already means the author has some general direction to go in. Like all things in fanfiction, when handled badly the OC Stand-In can delve straight into Mary Sue territory. Compare with the Possession Sue.

Sometimes these characters are just used to insult the heroes and make life hard for them, giving the character little point. Does Harry Potter really need another teacher who's out to get him? Hasn't Naruto dealt with enough crap already? In these cases, the character is simply used to replace the Canon obstacles for The Hero with smaller and (sometimes) more realistic ones.

An OC Stand-In is sometimes used to save a main character from being bashed... The OC Stand-In is then bashed instead, like, e.g., in many Naruto fanfics people make Sakura's mother responsible for her being a Fan Girl and an Alpha Bitch and let her make an whole laundry list of crimes against Naruto and the village.

However, there are cases, even when the OC Stand-In is "high school evil", that these characters turn out likeable. Or, at least, the Fanfic does.

In video games, sometimes the canon protagonist is an OC Stand-In, due to being a Featureless Protagonist, a Heroic Mime, and/or a highly customizable RPG player character.

A particularly successful interpretation of one of these sometimes ascends into Fanon when other fans want to play with that version.

Anime and Manga

 * Odd example from Infinite Stratos, it was the resident Harem Hero, Ichika himself, often being accused of being flat and dense. For the most part, it also doubles as Possession Sue, and packed in tandem with Adaptational Badass. The odd part mentioned because it's almost guaranteed that most people liked the change.
 * Tenten from Naruto is an archetypical example. Her brief appearances in canon provide enough character elements for fanfic writers to build upon, and yet she never even got a formal introduction. Being beaten by Temari -- off-panel in the manga—is her most memorable scene. Naruto author Kishimoto admitted that she was created simply to be fill the spot of token female on Team Guy.
 * Kishimoto, oddly enough, said he likes her design most out of the female ninja.
 * Sakura's parents, particularly her mother, are common Fanfic characters. And her mother is usually both a Straw Civilian and a total bitch to Naruto. She's become someone the Naru/Saku shippers can use as a Freudian Excuse for Sakura, or just plain hate for no reason.
 * Sakura's mother is heard off-camera in the anime, but she only seems to exist to prove that Sakura, unlike Naruto and Sasuke, had a normal childhood.
 * Other members of the Seven Swordsmen of the Mist show up often as oneshot villains. They're not even real characters to stand in for, so much as placeholders where characters presumably go.
 * Similarly, tailed beast hosts number 2 and 4-7, as two and four were only seen briefly while the others were . The fact that the author made full designs of all of them (even for the three-tail host, when the three-tailed beast didn't presently have a host) for a cover as part of a Milestone Celebration is pretty much asking for this—though ironically at least one of them has been given a plot-relevant backstory post-mortem.
 * Yugito Nii (the 2-tails host) is an extremely popular OC Stand-In, and is a frequent shipping target for Naruto.
 * Also, Hanabi Hyuuga, Hinata's sister, who only speaks in one scene and primarily only asks questions of her father. Fans tend to differ on whether she would become the heir or a branch house member (and how well she would accept either), and whether she loves Hinata or sees her as worthless.
 * Or, for that matter, sees her as a threat - the natural consequence of the prospect of one sister enslaving the other or else dying.
 * Dragonball Z: Vegeta's father gets this treatment. He's been dead for years and gets three scenes total over the course of the anime. He gets another in the first Broly movie, but if you count it as canon (which requires some shoehorning) it's a Moral Event Horizon. He shows only bare hints of personality. Yet he's also the subject of fan devotion that's surprisingly intense, if small in scale. (Vegeta's Missing Mom is also the subject of much speculation.)
 * Goku's Missing Mom too.
 * It's believed to be Fasha (which was not confirmed in any way). She gets this treatment too.
 * Since we're at Fasha, all of Bardock's teammates.
 * Happens very often in Axis Powers Hetalia fandom with nations that have only appeared in profiles or on the author's blog, especially since fanfic writers can research these nations' histories and stereotypes to come up with some technical canon. Some of these common fan characterizations are:
 * Denmark as a Boisterous Bruiser and Norway as Tsundere for him because of their long history together; the former turned out to be pretty spot-on with canon, while the latter is still up in the air (though Norway did strangle Denmark with his tie in one strip).
 * Belgium as a sassy, fearless Shorttank who enjoys waffles and chocolate and can drink anyone under the table; this turned out to be fairly accurate to canon (although she's more cheerful than sassy) with the Bottle Fairy part being the only one left unconfirmed.
 * Netherlands as similar to Denmark in personality with a pot-smoking habit; this was one of the Fanon characterizations that ended up Jossed by canon when Netherlands was revealed to be a mainly blunt and stoic Perpetual Frowner, though the smoking habit was pretty much confirmed.
 * Hong Kong as an Emotionless Boy with a penchant for pranks and snarkiness; this was mostly confirmed by canon, although he doesn't seem to be quite as emotionless as fanon loved making him out to be.
 * Taiwan as a Yamato Nadeshiko with romantic feelings for Japan; the Yamato Nadeshiko part was Jossed with the Drama CD (and more recently, the fourth manga volume) showing her to be a Plucky Genki Girl, and she doesn't seem to act much differently with Japan than she does with her other Asian siblings.
 * Vietnam as a Tsundere Tomboy who uses her rice paddle as a weapon or a Broken Bird emotionally scarred by her wars; it looks like her canon self will be more subdued than either of these characterizations.
 * Thailand as a Nice Guy who also happens to be a Bare-Fisted Monk that sometimes uses a Cool Sword as a weapon. He cooks well and loves spicy food, and lastly, no matter how nice a guy he is, he is ALWAYS portrayed as Cute and Psycho.
 * A few times, he's a Wholesome Crossdresser (thanks to RL Thailand's kathoey, or ladyboys).
 * Romania was almost always depicted by fans as a female (probably because of the potential Les Yay between her and Hungary), only to have canon Joss that with the fourth manga volume establishing him as male.
 * And with the canon Romania appearing to have red eyes and Cute Little Fangs, it's becoming common to depict him as either a vampire or an ordinary human who pretends to be a vampire for the lulz. It also helps that Romania is the country Transylvania is located in.
 * New Zealand is almost always depicted as either having a Vitriolic Best Buds or True Companions type relationship with Australia.
 * India, like Romania, was almost always depicted as female in fanworks only to be established as male later on in canon. No one seems to really care, though, probably because of his awesome Bollywood entrance in Hetaween 2011.
 * For a long time, Bulgaria's only canon scene was him hitting Italy with his stick and the most common fanon depiction of him was as a Jerkass with a Hair-Trigger Temper. This seems to have been Jossed, however, with him being shown in Hetaween 2011 and Hetalia Bloodbath 2011 as a fairly nice guy who's good friends with Romania.
 * Matt from Death Note is a good example of this. He gets little time on the page in the manga, and even less time in the anime, but he has a large fan base, and thus many people end up writing about him, usually just writing him as whatever they need, within limits, for the story.
 * Also Linda, who was mentioned in the manga a grand total of twice, seen only once, and has only one line. Considering that, she is a massive Ensemble Darkhorse; if you type in "linda death note" on deviantART you get 526 results, and she has 34 fanfictions on fanfiction.net.
 * Though they go unnamed in the manga, Ranma ½ has Ranma's buddies Hiroshi and Daisuke, and for the girls there's Akane's friends Yuka and Sayuri. They mainly exist to be Those Two Guys. Rumiko Takahashi seems to love this trope, especially in Ranma. Herb's got Mint and Lime. Kima has Masara and Koruma, and is herself not much developed beyond her role as Saffron's bodyguard. The Anime also gave us Kaori Daikoku, who appeared just once in the anime and yet comes up rather frequently in fanfiction.
 * From Neon Genesis Evangelion we have Kyoko Soryu (we have no idea what she was like before the incident, or even what the woman looks like) and (to a lesser extent, due to having somewhat of a discernible canon characterization) Yui Ikari.
 * Also, Class Representative Hikari Horaki's sisters, Kodama and Nozomi; they never appear on-screen, and the only known facts about them are that they're older and younger (respectively) than Hikari . To a lesser extent, Hikari herself. Also, Touji's little sister.
 * Occasionally the few Evangelion Canon Foreigners (such as Mana Kirishama) can fall into this, since not many Americans have actually played the games they appeared in. Mari Illustrious Makinami was this for some fans before her actual personality was revealed, and even then there's still a lot about her that's completely unknown. This can make her an Epileptic Tree stand in.
 * The unnamed girl from Dissociation was often used as this in Haruhi Suzumiya fanfiction until the release of Surprise.
 * An odd variation happens in the Fullmetal Alchemist series, specifically the first one. During the movie, and around the end of the show, Ed gets sent to "our" world where everyone he knows has an Identical Stranger. Fans have a ball with the unseen ones such as Winry's, who is usually portrayed as the opposite of tomboyish counterpart and is either a Dark Fic Replacement Goldfish or someone Ed learns to love, and Roy who is almost always portrayed as the Jerkass.
 * Lelouch of Britannia is prone to taking minor, undeveloped (and sometimes thoroughly unsympathetic) characters from Code Geass canon and giving them personalities, backstories, complex relationships with existing characters, and major roles. In some cases (particularly Kewell and Darlton), this results in their being Rescued from the Scrappy Heap.
 * Also in Code Geass (though not in the above fic) Kallen's brother Naoto Kozuki sometimes get this treatment, largely because all we know about him is that he was the leader of Ohgi's group and died sometime before the series started.
 * In Yu-Gi-Oh! fandom, there was a brief period of time during which people knew about the Toei series, but had no fansub available. Cue Miho, who was a one-shot character in the manga and had a prominent role in the anime, becoming an OC Stand-In, though her personality did often overlap with the one she had in the manga.
 * Example from Tengen Toppa Gurren Lagann: Nakim, one of Yoko's pupils, stars in his own story in the fic The World Tree.
 * This is heavily subverted with the series Zatch Bell, where unless you're Zatch, Tia, Zeon, Sherry, Brago, or another of the main characters, you'll never get any actual writing or stories based around you. Case in point, any of the many villian-a-week enemies of other mamodos Zatch faces. This extends to major recurring enemies as well.
 * A lot of the unnamed Posthumous Characters in Kirby: Right Back at Ya! get this treatment in fanfiction.
 * Sword Knight and Blade Knight get this a lot, too.
 * There are many characters in Kinnikuman that never show up again or barely get a chance to shine in the original manga. As a result, Matayan is forced to make up movesets for these characters in Kinnikuman: Muscle Fight.

Comic Books

 * This X-Men fic is one of the rare Possession Sue cases. It takes a very obscure character (Magneto's canonically-dead wife Magda) and turns her from a meek woman whose only real moment of characterization was fleeing her husband after he accidentally killed a bunch of people into a de-aged (since, as a Holocaust survivor, she should be fairly old, even with Comic Book Time) genius roboticist mutant with a power that's supposedly completely unique and desirable enough that people would kidnap her for it (despite there already being a canon character with the same power whom no one makes much of a fuss over).

Film

 * The Pirates of the Caribbean movies gave no name, characterization or any information about the mother of James Norrington other than she exists (because everyone has one). The Mega Crossover fancomic Roommates made her an extremely likable Irish Cool Old Lady.
 * Unused or non-canon characters from The Lion King series are especially apparent in fanon works. The most common are Mheetu (Nala's brother), Kopa/Fluffy (Simba's son), Tesma (a meerkat friend of Simba), Naanda (Sarabi's sister), and Bhati (a bat-earred fox friend of Simba). Given that most of them don't have much of a personality this leads fan-artists to create their own versions.

Literature

 * Professor Aurora Sinistra from Harry Potter.
 * Blaise Zabini gets special mention here since from his name appearing in book one until he got a physical description in the book six, half the fanfic writers assumed it was a girl's name (They've since taken to writing about Daphne Greengrass or Tracey Davis when they need a generic Slytherin girl.)
 * This even applies to translators. In the Dutch translation, names are frequently changed to sound more familiar to the readers. So a Bella Zabini was sorted in book one, and in book six 'she' magically became Benno Zabini.
 * The other half thought he was some type of Italian Sex God. Just imagine the reaction when it was revealed he was black.
 * The Italian Sex God thing actually worked out pretty well. Canon Blaise gives the impression of having the same kind of "player" personality as Italian Sex God Blaise. Plus he was assumed to look swarthy, being Italiain. Basically, you can just take Italian Sex God Blaise, darken his skin color a few notches, and suddenly he's canon.
 * Daphne Greengrass also gets a lot of attention when authors need a sympathetic Slytherin girl, as she's rarely if ever mentioned in the same negative light as Draco or Pansy in the books. Typically she's said to come from a neutral wizarding family or otherwise isn't connected with the rest of her house, possessing the same traits that Slytherins are known for but without invoking Ambition Is Evil.
 * Really, just take any throwaway name mentioned in the series and you'll find at least a few dozen fanfics starring that character.
 * Chris Columbus giving his daughter Eleanor a cameo by casting her as Susan Bones in the first two movies might almost count as an "official" version of this. After all, Susan was a background role with no lines, so what better place would there be for the American director to slip his daughter in without effecting the all-British cast requirement? Well, true to form, Susan ended up getting developed into more than just a throwaway name in the books written after the first two movies came out. The latter films handled this by simply not including her plotline, which they likely would have done anyway considering the length of the latter books. In any case, if they had really wanted to include her in Phoenix or Prince with actual lines, they presumably would have just invoked The Other Darrin.
 * Back before Ginny had much of a canonically defined personality, she was a frequent target of this.
 * Fanfic writers are also fond of writing about the main characters' kids' school days, when they don't just ignore the epilogue entirely.
 * Aeneas has a very minor role in The Iliad, but Virgil made him the protagonist of his Aenead, partly because he was such a blank slate and partly because he was one of the few Trojans to survive the sack of Troy. This makes this trope, you guessed it...
 * Rosencrantz and Guildenstern - very minor characters in Hamlet - become the protagonists of Tom Stoppard's Rosencrantz and Guildenstern Are Dead.
 * In Peter Pan, Jane appeared in only one scene and was basically a Generation Xerox of her mother, Wendy. The Disney sequel Return to Neverland turned her into a highly pragmatic, disillusioned girl who grew up too fast as a result of living through the bombing in London. Margaret, the next descendant in the Wendy line (named, but never shown), gets this treatment in some fanfics.

Live Action TV

 * There are Lost fanfics that takes the minor survivors, including extras, and gives them the full on Lost treatment, with flashbacks and their own sideplots.
 * Although the show itself wasn't above doing that, either.
 * Ronnie Gardocki from The Shield qualifies as a major example of a live action version, as fans of the character have largely grafted onto him the personality of good guy nerd/geek who fell in with the wrong crowd as far as personality goes. Ironically, David Rees Snell (the actor playing Ronnie) has joked that had the writers fleshed out Ronnie and explored the character's dark side in relations to him being just like Lem, Shane, and Vic as far as being a Jerk Jock, that he probably would have lost all of his fans.
 * iCarly: Rebecca Berkowitz, seen only once, in an extended rarely seen version of "iSaw Him First" and usually mentioned off-handedly. In any fic with her as a character, she's basically going to be an OC with a canon name, if they even bother to develop her past the implied Really Gets Around.
 * To a degree, the Eighth Doctor from the FOX Doctor Who movie, at least when compared to the rest of Doctor Who continuity. Since the movie was a failed pilot, this Doctor received nowhere near as much character development as other Doctors, and ended up becoming something of a Tabula Rasa. As a result, he has seen the most fanfics and extra media (comics, audio plays, novels) of any of the pre-2005 incarnations.
 * On Neighbours, Lisa Jeffries was a very minor character who shared a few scenes with Summer Hoyland; she appeared in about a dozen episodes over the course of two years. She has, however, inspired a substantial volume of fanfic, which has developed her in ways totally unrelated to her canonical characterization.
 * A juvenile character named Marissa Flores, who appeared in the Star Trek: The Next Generation episode "Disaster" (and absolutely nowhere else in Trek canon), spawned the rather infamous Marissa Picard fanfic series, written by a chap named Stephen Ratliff. And it's not limited to just Marissa; Ratliff also included a bunch of one-off kid characters from TNG as the title character's various minions and cohorts.
 * In the Thirty Rock fandom, the Liz/Gretchen ship has a sizable following. Even if you're regular viewer of 30 Rock, you're probably wondering who Gretchen is. Well, she's a "brilliant plastics engineer/lesbian" whom Liz was set up on a date with as part of a Mistaken for Gay plot. Gretchen appeared in one episode back in the first season and has not been seen or mentioned since. But let's face it, it's not hard to see the appeal of pairing someone who looks like Stephanie March with someone who looks like Tina Fey. Plus, the episode contained a substantial amount of Les Yay, featured Frank and Pete becoming Shippers on Deck for Liz/Gretchen ("So you're saying I should just be a lesbian?", "I'm not saying it'll be easy. You get drunk first."), and ended with Gretchen deciding she couldn't be Just Friends with Liz because they were getting into a Stupid Sexy Friend situation.
 * Puck's mother and sister on Glee, since they don't even have names in canon, but he presumably lives with them and they therefore play at least a minor part in most fics about his life outside of school and glee.
 * Since Sebastian Moran (Moriarty's leutenant in the original Doyle stories) has no canonical characterization in Sherlock, he's effectively become one of these for the fandom. He's been depicted as everything from Affably Evil to a Domestic Abuser to a Dark Action Girl.

Music

 * Vocaloid, naturally, since there is nothing canon about the singers, besides name, voice and appearance (and sometimes not even that).
 * One story managed to bring in one of the character's creator as a separate character.

Newspaper Comics

 * The Little Red-Haired Girl from Peanuts is an unseen character, though she made a few tantalizing non-canon appearances in television specials), and we know nothing about her personality since Charlie Brown doesn't have the guts to talk to her (and, hence, really knows nothing about her himself. Any time she appears in a fanfic, she is this trope by necessity.
 * Peanuts is actually full of minor characters who get used as OC stand-ins. Of particular note are Franklin, Violet (usually Alpha Bitch, especially in stories that require Lucy to be slightly nicer and need a replacement villain), and Shermy (whose character trait in most fanfics is having no character traits at all, unless he's The Ace to Charlie Brown as he was in several early strips).

Toys

 * This trope is all over the place in Transformers. The franchise is filled with characters who only appear as toys with bio notes of varying character depth. It has even happened in canon on a few occasions - the profile book More Than Meets The Eye required the authors to invent personalities for the Micromasters out of whole cloth, since those characters did not have bio notes.
 * Many fans were actually thrilled when this was done, en masse, in the canon comic Transformers: Last Stand of the Wreckers. Japanese exclusive Overlord and toy-only characters Pyro, Ironfist, Guzzle, and Rotorstorm were assigned new, quirky personalities and pretty much became fan favorites overnight. Well, Guzzle had been used in comics before, just in a negligible, minor role.
 * The same applies to Bionicle and its Loads and Loads of Characters, some of whom only appeared in a scene or two and barely get to be described (the author claims he is very bad at coming up with visual traits, for example). The developers of the beloved Mata Nui On-Line Game said that LEGO barely gave them the most minor of side-characters to work with, and they had to develop their personalities and culture themselves. What resulted was a game teeming with characters more memorable and charming than many of the ones that the "official guys" made up. They easily became fan favorites.
 * Fans themselves also get chances to flesh out some of the more underused characters, via official writing or art contests. In the latter, they can even design the look of the characters themselves.

Video Games

 * Any Heroic Mime character tends to be this, due to little to no characterization of them in the actual source material.
 * Just about any Pokémon fanfic that places characters from the games (Brendan, Lucas, Silver, Leaf, etc.) into the anime's continuity will make use of this principle to some extent, since most of said characters never appeared on the show outside of 3-second cameos, with Leaf never appearing at all. There's no set pattern for what personalities writers assign them, but there's usually a good chance that they will be used for Shipping somehow.
 * Likewise with game fanfics themselves. No one takes account to Dawn or May's in-game personalities, being that they're technically not their canon ones though. Most NPCs get this treatment to various effects. Rivals and protagonists are given whatever personality, being that you really have to look into the text of the games to see any bit of personality beyond "Hot-Blooded, determined Child Prodigy".
 * Due to the fact player characters and rivals can be named by the player, fic writers can freely use any name for any of the above characters, except possibly Brendan and Lucas in the anime. For some reason, writers tend to use their own names for these characters.
 * The Generation IV Frontier Brains (other than Palmer and Caitlin, who have appeared outside the Frontier in the games) rarely appear in the anime continuity, but when they do, they are this trope.
 * Commonly done to Dark Link from The Legend of Zelda. In the video games, Dark Link is a mindless, monstrous, obstacle, usually representing the evil in Link. But fanfiction writers and fanartists tend to give him a face and personality.
 * Link himself, whose dialogue is limited to the player picking 'yes' or 'no' when asked a question (and "no" usually gets you a re-statement of said question) lends himself to this. The main character of a video game is often a blank slate for the player to write him/herself onto, after all.
 * Touhou has this mainly in the form of the dialogueless midbosses. The standouts are Daiyousei, Koakuma, and Momiji, who have managed to become fairly popular. Most of the time they remain Satellite Characters to the boss whose stage in which they appear.
 * Daiyousei and Koakuma don't even have any stated non-danmaku powers in a series where virtually everybody has a random superpower, so fans are required to make up a power for them. They didn't even have names originally, the ones used here invented entirely by the fandom (translated as "big/greater fairy" and "little devil", respectively).
 * Part of the reason for the massive doujin and fanfiction community that has arisen around the games is that, despite the Loads and Loads of Characters, only a small portion of the cast receive anything more than a brief character profile and some dialogue, and even fewer receive any form of backstory, leaving writers with enormous wriggle room. Even the two Universe Compendiums are written by Unreliable Narrators working with a lot of second- and third-hand information, and ZUN himself is notoriously unhelpful and even outright contradicts himself. Most of the widely accepted interpretations (for example Marisa and Alice as friends, the existence of Team 9, Reimu experiencing Perpetual Poverty, Yukari as the God and Ruler of Gensoukyou) are not even hinted at in the games but remain entirely plausible.
 * Doctor Cain usually gets this treatment in Mega Man X. Despite being a pretty important canon character in regards to the backstory, he barely gets a few lines in the games before vanishing. Most fanfic writers characterize him as a kooky old man and a father figure to X and Zero. Lots of other characters could also qualify, since the MMX games were very sparse on characterization until the later games.
 * The same can be said for the characters in Mega Man, since most of them only have a small character profile to hint at their personalities.
 * The Guardian Spirit from the first Baten Kaitos game is supposed to be you, and is therefore a sort of Featureless Protagonist. Naturally, there have been several fanfics written about the this character. Unfortunately, too many of these fics end up making the Spirit a female Mary Sue with a crush on Kalas. The term "Spirit Sue" was created by the fanbase to describe this particular interpretation of the character.
 * from the prequel doesn't get this to the same degree, since he has an actual role in the plot. However, he could still work for this trope, since his actual personality is never shown.
 * The commentary on Half-Life 2 states that this is the entire point of Heroic Mime Gordon Freeman, with the player being the OC in question.
 * Resident Ensemble Darkhorse Adrian Shephard as well. All we have of his personality are a few diary entries in the Opposing Force manual which don't say much.
 * The same is true of Chell, the protagonist of Portal. The few things that we're told about her character are likely to be complete lies, so any characterisation in fanfic is made from whole cloth.
 * Decoy Octopus from Metal Gear Solid is one of these, especially since it's part of his job description. He literally can adopt the personality of whoever he's disguised as.
 * Metal Gear Solid 3: Snake Eater has a whole group of these in the form of the Cobra Unit. Several fan writers/artists have done their takes on the Cobra Unit who, in the game, have a total of about three minutes on screen outside of the battles with them. They are one of the most popular topics of MGS fanfic, especially among female writers.
 * The Forerunners from Halo are practically an entire species (or group of specieses) of OC Stand-Ins. The upcoming trilogy of novels should shed come canon light on them, though. Til then, fanfic portrayals of them remain wildly varied.
 * The Rookie in Halo 3: ODST is this to a lesser degree, having no lines beyond grunts, no visible face (he always has his helmet on), and no identification beyond the initials "JD"; the designers claim this was intentional, to better allow the player to integrate with the character. Spartan-B312 in Halo: Reach is this even moreso, with male and female voice sets, and armor customization that is persistent throughout both campaign and multiplayer; this was done for the same reasons as the Rookie.
 * The "Library Girl with a Pigtail" in Final Fantasy VIII, who crushes on Zell and seems to have his interest by the end of the game, yet who remains nameless and without any personality beyond "bookish and shy" in canon. Begs for Possession Sue treatment by any Zell fangirl.
 * The Nasuverse has several characters only mentioned in backstory that aren't very well described. Thus when these characters are used in fanworks, the trope is present. Perhaps the biggest example is Altrouge Brunestud, Arcueid's sister. We don't even know what she looks like (beyond that she looks like a fourteen year old girl), but that doesn't stop the fanart.
 * Odd canon example, Dissidia Final Fantasy, a crossover that featured characters from the first 12 Final Fantasy games, had to pretty much create personalities for the Warrior of Light and the Onion Knight from the wholecloth.
 * Mass Effect fanfiction has Oriana and Kolyat, Thane's son, as a relatively popular pairing despite never meeting, or even coming close to meeting and having no connection to each other in the game besides a certain Commander intersecting with their lives. Kolyat is developed a bit better than Oriana, who never actually speaks or is interacted with.
 * Preitor Gavorn -a turian whom you only meet outside of Afterlife- is this to an extent, too. He was largely ignored by the fanbase for some time, until a video in Lair of the Shadow Broker showed him with a human male in what appears to be a bedroom. Since then, he has been given varying personalities, though most have some hints of Invisible to Gaydar in them.
 * Annother popular target for an OC Stand-In is Hanna Shepard, the Player Charicter's mother if the spacer background is chosen.
 * Sonic the Hedgehog has accrued several such characters, though since these often turn up in the comics, said personalities are often used. Nevertheless, Ray the Flying Squirrel, Mighty The Armadillo (though he's almost always put as the lost forth member of Team Chaotix), Bean the Dynamite, and Bark the Polar Bear (often paired together, for being introduced in the same game), often end up being OC stand-ins, as do Ashura The Hedgehog, Wechnia, Tiara Boobowski, Nazo, and Honey The Cat, though these five are very rare to see in fanfic, not that the first four show up often, Original Characters are far more common.
 * A few shopkeeps from The World Ends With You get this treatment, and HT Masuoka in particular is a favourite of slash writers given his suggestive dialogue. Eri is the minor character who gets the most mileage by far, however, since she has a confirmed pre-existing relationship with Shiki and can be believably integrated into the main cast.
 * Kaede from .Hack://GU has absolutely no real importance in the story other than acting like Zelkova's bodyguard, although until she joins your party in the post game you have no idea what her weapon even is. The worst part is she basically vanishes in volume 1 after her appearance, yet you can still do the marriage event with her in Volume 3 despite her having absolutely no development and virtually no game time.
 * Player Mooks can easily be used as this.
 * Fire Emblem has the tactician from the seventh game. His default name is Mark, but you can change that and his gender. He never says anything (that we hear) and is only spoken to. There are a small wealth of fanfics about him/her, and almost each one gives him a separate personality and back story.
 * The originally-intended but eventually scrapped protagonist of Psychonauts, Dartagan, appeared in the game for less than five seconds. There is a huge range of interpretations of him within various different fanfics, roleplaying accounts, and even Creepypasta.
 * The player characters from the Harvest Moon series, being Silent Protagonists who's only real characterization is "friendly and hard working." Real OCs only come into the picture when fic writers want an exotic-looking character (90% of the time, female).
 * The Pyro of Team Fortress 2 often gets this treatment, having the least characterization of all of the classes, no backstory, or even a set gender. This practice will presumably stop when his/her 'Meet the' short finally comes out.
 * In Katawa Shoujo, the students in Hisao's class besides him, Shizune, Misha and Hanako get this treatment, as a piece of official art shows their names, club affiliations and disabilities, but nothing about their personalities or backstories.

Web Comics

 * The Midnight Crew Intermission of Homestuck brought us The Felt, a 16-man mafia group, only two of whom (Snowman and Doc Scratch) got substantial characterization to be clearly defined as characters. The rest of the fourteen ALL get this treatment, as only their powers and maybe a single moment of funny is supposed to encompass their characterization. The only exception is Clover, whose appearances manage to characterize him as a fusion between The Riddler and the Clock King, which is still a fairly open characterization.
 * Until recently, two of the Felt only appeared posthumously, and all that was known about them previously were their names and faces (of course, they still got no characterization at all when they showed up). While their appearances in fanfiction increased once they made an appearance in the story, there still were examples of people using them for as OC Stand-Ins before anything was known about them.

Western Animation

 * Phineas and Ferb: Until episodes such as "Isabella and the Temple of Sap", the Fireside Girls had close to no lines and no characterization, other than Gretchen, who even then only spoke once or twice.
 * Especially Gretchen, who in Fanon is often paired with Ferb, apparently just because she's the first girl his age (other than Isabella) to get a name.
 * Ezekiel from Total Drama Island gets this fairly often; he got very little development because he was the first character to get voted off, an event that some viewers thought was unfair since he had completed the episode's challenge while other characters didn't. To a lesser extent Katie and Sadie also get this, since in canon aside from their co-dependency they have very little that separates them from the more developed and funnier Lindsay.
 * Gretchen on Invader Zim. In canon, she was strongly hinted to have a crush on Dib in one episode. The pairing is not widely popular (despite being the only romance in an otherwise No Hugging, No Kissing series), but even those who don't use her as a main character often elevate her to "Most Important Random Skoolkid" or mention her and Dib's "romance" in passing.
 * Another commonly used character is Invader Tenn; she only shows up in two scenes in one episode, and it was planned for her to return in the never developed series finale. Because of this, she is very often often used whenever a writer wants or needs to use an Irken outside the ones with more screen time (Zim, the Tallest, Tak, Skoodge). Of course, most of the stories she shows up in are based on (or are outright fan versions) of the aforementioned finale.
 * Zita is another victim to this. While a girl with her looks is common to see in the episodes, all we know about her is that she considers Dib to be crazy and, unlike other students, is respected by Ms. Bitters. Nevertheless, people throw even this minor canon out of the window and pair her up with Dib. That's how terrible they are.
 * The Metalocalypse fandom has Klokateers. In the show, they're several legions of hooded, uniformed, fanatically loyal employees of the Dethklok company who rarely have lines and are referred to by number rather than name. Because of the extremely stringent entrance exam and its 50+% mortality rate, the recruits who survive to become Klokateers are extremely exceptional specimens, physically and intellectually. This makes them ripe for this trope. There are a few who have risen to prominence, mostly through slash fandom.
 * Daria fandom is pretty notorious for this, largely due to the fact that the show has scads of random recurring backgrounders who never do anything and yet have extremely distinctive character designs (a result of them all being based on real people who worked at MTV at the time). Because the fandom is relatively close-knit, the characterizations of many backgrounders have actually become pretty standardized. Burnout Girl is almost always involved with drugs, that blond from The Invitation is named Tori Jericho & was president of the Fashion Club before Sandi, etc.
 * This is common in the My Little Pony Friendship Is Magic community, due to the prevalence of Ensemble Darkponies. Many of the most popular characters in the fandom have no official names or speaking roles, let alone a canon characterization. Some of them have appeared onscreen for only a couple of seconds in a single episode.
 * Special mention goes to Princess Luna. When she finally appeared in Season 2, she left this trope behind by contradicting nearly every fan depiction of her.
 * It's common with the other series too. There are dozens, maybe even hundreds, of toy characters that either didn't pop up in the cartoon adaptations or didn't get much screen-time at all (many didn't even speak). Thus people make up whatever personality they want, especially in later gens where few characters actually have real backstories anymore.
 * X-Men: Evolution is an unusual case, as it's not so much characters from the show who're stand ins, but the characters not featured. Due to the series tweaking some personalities to make them teenagers (some who all they share with their original versions being their names and some don't even get their real names, just their old codenames), a lot of characters from the comics that the show was based on work as these. Want a female British X-Man? Covered, Betsy Braddock/Psylocke will work. Want a male British one? Pete Wisdom. Want a team genius? Cither. Want a character with a dark and edgy past? Its X-Men, anyone would fit that.
 * Dani Moonstar and some of the New Recruits serve as this as well. As Dani only appeared in one episode, not much of her personality was fleshed out, and as such can serve as any personality type they want. Roberto only got a bit of characterization: A slightly egotistical 'jock' type, while Rahne got a snarky playful personality, both from just one episode, after that, they get no lines other than background appearances.
 * Ursa, Zuko and Azula's Missing Mom, from Avatar: The Last Airbender. She's of no small importance to the plot, given that she, but her only scenes are in Zuko's flashbacks and  . Fans have a field day discussing how accurate either of those are and what she was actually like. It doesn't help that the lack of a family reunion is the series' biggest unresolved plot thread.
 * Danny Phantom has a few, but none so popular as Star, or Star "Satellite" as the fandom has named her. She has some lines and establishing character moments, but in general, the Show portrays her as the blonde girl who hangs around the Alpha Bitch Paulina. Naturally, fanfic authors have a ball giving her Hidden Depths.