Not all characters are important to a story. However, those that aren't are normally not developed that well, while plot relevant characters are. On the other hand, sometimes it can go the other way, and minor, undeveloped characters (or a two dimensional main character) can set the plot in a new direction. This trope takes that to its logical conclusion.

This character has an effect on the plot; however, they're never introduced or named or possibly even shown in the background. This is usually the result of them being a RedShirt or UnwittingInstigatorOfDoom in someone's backstory (so what they did or what happened to them is only relevant for how it influenced the character whose backstory they appeared in). However, in the most extreme examples, their existence may only be implied (for example, someone who left their MacGuffin or EmergencyWeapon lying around for TheHero to find).

Note that while this character ''might'' be revealed and fleshed out later, there isn't usually any mystery about who they were; their role is fulfilled just fine by them being just another face in the crowd and they need not have any further effect on the story. The best way to identify a character as this trope is if they can only be referred to by their contribution to the plot and in the past tense, making it clear that they're little more than the reason something happened (e.g. "That guy who [[StarterEquipment gave]] Bob his sword" or "That [[UnwittingInstigatorOfDoom urchin]] who stole Alice's wallet when she was buying her dead sister's medicine"). Indeed, the only reason they exist is the fact that they did something that had to be done by ''someone'', and in this case that someone was nobody important.

Compare TheGhost, who functions as any other character would (and might even be part of the main cast) but is simply never shown on screen (they can overlap; the main difference is that characters who fall under this trope don't have any characteristics, while the ghost can still be a fully fleshed out character), PosthumousCharacter for already dead characters who are still important to the plot, and the FeaturelessProtagonist, who can become this trope in sequels. A BadassBystander will often become this if they don't appear subsequently and aren't given any characterisation beforehand. If they become a recurring character in later works or adaptations, they will often evolve into HeWhoMustNotBeSeen or TheGhost as a nod to their earlier characterisation (or lack thereof). Contrast LowerDeckEpisode and DayInTheLimelight for when less developed characters are fleshed out by the plot. Often overlaps with a CrypticBackgroundReference or DiabolusExNihilo (for malicious examples).
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!!Examples;

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[[folder: Anime and Manga ]]

* In ''GhostInTheShellStandAloneComplex'':
** [[spoiler:Aoi]] aka "[[AntiVillain The Laughing Man]]" reveals that he himself was arguably the second part in the eponymous "Stand Alone Complex" (an event where many people spontaneously start copying something which wasn't there in the first place) and the real "Laughing Man" was [[spoiler: an unknown person whose email exposing the micromachines company's coverup was found by Aoi.]]
** In the episode "Embraced by a Disguised Net CAPTIVATED", a member of an OrganLegging gang accidentally kidnaps the daughter of a politician who was denying their existence. The rest of the gang are never shown, but it turns out the entire episode's plot was orchestrated by [[spoiler: a rival who had given her a list of kidnapping targets which included the girl so she'd be branded a traitor.]]
* The second generation of ''GetBackers''. They give Ban and Ginji their name, their car, and their analogy of a retrieval being like a jigsaw puzzle, but the only reason they exist is because the identity of the ''first'' generation is a major plot twist and a surprise to the cast.
* In the background of ''Manga/FullmetalAlchemist'', the War of Ishvalan Extermination was caused by the Ishvalans uprising against the Amestrian military. It's later explained that they did this because an Amestrian soldier shot and killed an Ishvalan child for no discernible reason, but no one knows who this soldier was and the Amestrian military claim that the Ishvalans made him up as an excuse. [[spoiler:Later still, the trope is actually subverted when it's finally revealed that the "soldier" was the disguised homunculus Envy, who deliberately started the war as part of the BigBad's plan.]]

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[[folder: Comic Books ]]

* Joe Chill, the mugger who murdered Bruce Wayne's parents, sometimes functions as this, particularly if his identity is still a mystery to {{Franchise/Batman}}. In other versions of the story, Bruce eventually finds him and he gets dealt with.
* The ([[SpiderMan3 usually]]) unnamed robber who killed SpiderMan's uncle Ben. He's literally responsible for Spidey's entire career, but he's generally only ever referred to as "the robber" or "the burglar."
* Whenever the GreenLanternCorps appears in force, the background will be littered with unnamed Lanterns who exist simply to fill out the Corps' numbers and give the artist an opportunity to draw weird aliens (and give the bad guys Lanterns to kill other than the ones with names and speaking parts). Sometimes one will strike a chord with an artist or the readers and appear enough times to get a name, but many will only ever appear in one issue, or even one panel.

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[[folder: Film ]]

* The BigBad of ''TheUsualSuspects'' is one "Keyser Soze," who very few people have ever met firsthand and lived to tell about it -- the only one the police have tracked down is a mutilated Hungarian sailor babbling nonsense. We see him with his FaceFramedInShadow, but even that is only within the {{flashback}}s of a [[UnreliableNarrator questionably-reliable narrator]]. We hear his OriginStory, but it's the kind of unlikely, mythologised tale you'd expect of a FolkHero. The only contact he has with any character is via TheDragon, Kobayashi. The final [[TheReveal Reveal]]? [[spoiler: The narrator ''is'' Keyser Soze, so far as such a man exists.]]
* The sorceress in ''Disney/BeautyAndTheBeast'' who turns the prince into a beast and lays a curse over his entire castle, thus kick-starting the plot. We're given no explanation for ''why'' she does this - was she motivated by a sense of justice in putting the prince through a SecretTestOfCharacter, or was it DisproportionateRetribution at being rejected by him? She's also never seen in person, only depicted in stained glass at the beginning of the film.
* Many of the events of ''TheGodsMustBeCrazy'' happen because a pilot flying over Africa's Kalahari Desert - who is never named, never speaks, and appears for only a few seconds - thoughtlessly tosses an empty Coca-Cola bottle out the window.

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[[folder: Literature ]]

* Hoid is a mysterious character who has appeared in almost every one of Creator/BrandonSanderson's books; the only exceptions are the ''Wheel of Time'' (since they are not originally his books) and the Literature/AlcatrazSeries. He is seldom named, but inevitably the cause of something that eventually turns out to be instrumental to resolving the plot, even or especially if a story otherwise has no indication of being in the same universe any of his other books.
* King Galbatorix from the ''Literature/InheritanceCycle'' doesn't appear until the last book, yet he is a constant presence in the series.
* [[BigBrotherIsWatching Big Brother]] from ''Literature/NineteenEightyFour'' is technically the BigBad of the story; however, he's never shown in person and it's left up in the air as to whether he really exists in the first place. [[spoiler:The same goes for the leader of [[LaResistance The Brotherhood]] (where it's not even revealed whether the organisation he leads even really exists).]]
* In ''TheMalloreon'', there is an unnamed character who stole the Sardion (MacGuffin of the series) and deposited it at its final resting place to be found by the heroes 300 years later, along with his remains.
* In ''{{Rebecca}}'', the main character is the second wife of the eponymous Rebecca's husband. She's compared unfavorably to Rebecca without ever being told anything about her by his staff. Nothing is revealed abut her as they figure she doesn't need to know, except that she died. In the end the protagonist learns more about Rebecca and [[spoiler:gains the respect of the inhabitants by saving them from a fire]].
** In the film adaptation, [[spoiler:the head maid refuses to accept her and stays behind to die in the fire.]]
* In ''Literature/TheBible'', Cain had a wife, but her very existence is a notorious theological mystery, since Adam, Eve and the murdered Abel are the only other humans mentioned from creation until that point. She doesn't even get a name, even though both wives of Cain's great-great-great-grandson Lamech are named.

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[[folder: Live Action Television ]]

* Played with in one episode ''Series/DoctorWho'' ("Midnight"). The Doctor goes on a shuttle, and socializes with everyone in the cabin except the hostess. It gets lampshaded at the end when he realizes no one knew her name [[spoiler:after she [[HeroicSacrifice sacrifices herself to protect everyone]] from the MonsterOfTheWeek]].
* Vivienne in ''Series/{{Merlin}}'', who is also a PosthumousCharacter. She is the mother of Morgana and Morgause, was married to Gorlois, and had an affair with Uther. That's literally all we know about her.
* One episode of ''{{MASH}}'' features a helicopter pilot who risks his own life to fly patients to the unit with a broken fan belt in his chopper's engine. He gets a replacement and leaves again, and no one ever even has a chance to learn his name, much less thank him for his bravery. When the medical staff assemble a time capsule at the end of the episode, Hawkeye suggests including the broken fan belt to commemorate the man's courage.

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[[folder: Newspaper Comics ]]

* The Little Red-Haired Girl in ''{{Peanuts}}'', Charlie Brown's always offscreen, always silent, always unrequited crush. She was briefly shown and named Heather in one of the animated specials, but this is not canon. A 1990s strip showed her in silhouette, dancing with Snoopy.

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[[folder: Theatre ]]

* Godot in ''Theatre/WaitingForGodot'' drives the plot as the characters spend the entirety of the play...well, [[ExactlyWhatItSaysOnTheTin waiting for Godot.]]

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[[folder: Video Games ]]

* ''VideoGame/{{Bastion}}'' has a couple, the most obvious one being [[spoiler:the unknown man who seduced and betrayed Zia, which lead to both her surviving the catastrophe...and to her father setting it off.]] Another example would also be whoever ended up with The Kid's [[spoiler: money, which he'd been sending back to his mother (who was already dead). Forcing him to take another tour of duty as a Mason (although with the loss of his mother he might have done so anyway) and surviving the catastrophe.]]
* The [[FanNickname Rat Man]] in ''VideoGame/{{Portal}}'' who has scrawled graffiti all over the place (although he might be closer to TheGhost, given that he's essentially interacting with the story still). A comic given out with the game's sequel fleshes out this character.
* In the game ''VideoGame/{{Singularity}}'', you often come across hidden messages that seem to be addressed to you, specifically. The messages are from someone who seems to know you, and who also seems to have done the same things you're doing; before certain major plot points, the messages will actually give you the heads up before anything's actually evident (i.e. "DON'T TRUST HIM", etc). It's later implied to [[spoiler:be a future version of yourself who went back in time to leave the messages]].
* In ''VideoGame/QuakeIV'', the protagonist from ''VideoGame/QuakeII'' is this (Quake IV being the direct sequel to Quake II). He single-handedly invaded the Strogg homeworld and assassinated their leader, allowing a full-scale human invasion. He is never shown or mentioned by name.

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[[folder: Real Life ]]

* The soldier who fired the arrow which killed Harold Godwinson in the Battle of Hastings (thus changing the course of English history).
** That said, nearly everyone involved is this trope due to so much of the events being lost in the mists of time. One historical EpilepticTree is that the entire arrow-to-the-eye story was [[InvokedTrope invented specifically]] to overshadow the achievement of the (named) knights who probably killed Harold by hand.
* The "person from Porlock" who interrupted Coleridge while he was in the middle of writing "Kubla Khan". By the time he'd managed to get the person to leave, Coleridge had completely forgotten the dream that inspired the poem, leaving it forever unfinished.
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