Stan: Dude, I have a picture of Mysterion in my locker too.
Clyde: Yeah, so do I.
Cartman: What?! Why?
Clyde: I don't know, it's just a cool costume.
A standard fixture of the Fantastic Comedy: whenever the series concept requires that an extraordinary person Masquerade as ordinary, there is one person around who suspects them, or has already learned about their secret (usually not every little detail, but enough to see them for what they really are). This character is always the Only Sane Man — Clark Kenting, fortunately, still works for everyone else — making this character only look crazy if they try to expose the protagonist.
If the character himself is not convinced that they are just hallucinating — and some of them are — they become set on getting proof to show everyone else that they were right all along — only to fail every time. Sometimes the neighbor fancies herself an Amateur Sleuth, going so far as to spy and snoop whenever visiting the "undercover" character. They may even set traps to expose the character's Masquerade. Usually though they have no idea — or care — about the trouble they are getting themselves into around the protagonist, so typically the hero will need to save them when they get too involved. Some have a perfectly logical (though often villainous) motivation, but other seem not to have considered the question "What would happen if you did expose your neighbor's secret, and would you really benefit from this?"
This character is usually a normal human in the vicinity from their civil life who has noticed that something is odd or amiss with them — a Nosy Neighbor or a Snooping Little Kid. If the masquerading subject is in school, the character is quite likely to be a teacher at that school, or a School Newspaper News Hound. If the show is a Work Com, it can be a co-worker, often a rival or the subject's immediate manager.
Occasionally, the character will have had an obsession with the supernatural before they meet the protagonist. They may be a danger that comes from the outside — Hunter of Monsters, an Inspector Javert or the Intrepid Reporter.
Often there is a character around who could give weight to their claims, an authority to present their proof to who views with bemused indifference their ranting insistence that something is strange about the main character — a husband if the character is the neighbour, the school principal if they are a teacher, a more senior manager in a Work Com. Sometimes a sidekick whom they drag into helping them — usually an underling, such as a school janitor if or an intern — is also present.
- Fables did this twice; once when a reporter thought all the folks of Fabletown were vampires; and planned to "out" them to the world. The second time was with Thorne, later subverted because he's a Fable himself.
- Ben Urich was this to Daredevil, in both the comic and the movie adaptation.
- The Silver Age Lois Lane would occasionally act this way around Superman, as would Lana Lang around Superboy.
- Also Jimmy Olsen.
- Played for black comedy in a one-page story in an old Superman comic: Clark is reading a book at the Daily Planet when suddenly Lois Lane falls from a window. He rescues her without changing his clothes as Clark. Then she tells him this was the only way she could make sure Superman was Clark Kent. Next panel we see another reporter talking to Clark, again reading a book:
Clark, have you seen Lois?
Yes... she fell out of a window.
- In the Silver Age, Dick Malverne. He grew up at the Midvale Orphanage during the same time that Kara Zor-El/Linda Lee/Supergirl did, and he was constantly trying to prove she had super-powers. In Young Love, he revealed that he always knew Linda was Supergirl, but after a while he decided to keep it a secret.
- In Action Comics #361, a boy thought Linda Lee was Supergirl, and he pretended to be Kryptonian to goad her into revealing her secret identity.
- In Adventure Comics Nasthalthia "Nasty" Luthor — Lex Luthor's evil niece — enrolled at Stanhope University as a student, hoping to lure Supergirl out into the open so her uncle could kill her. Several issues later she is convinced that Linda is Supergirl and follows her to San Francisco, where both begin work as junior reporters for K-SFTV as she tries to out Linda/Kara. In Demon Spawn she even tries to out Supergirl while the Kryptonian heroine is trying to get her out of a burning building.
- Vicky Vale in Silver Age Batman comics.
- In the comic PS238 a school full of kid superheroes in their civilian secret identity disguises also includes the extremely paranoid Cecil Holmes, who is convinced his school is full of disguised aliens.
- Semi-subverted in that Cecil turns out to be a metahuman who can detect other metahumans and that was what was fueling his paranoia. Ironically, he never manages to spot the actual alien at the school, Prospero.
- One of these neighbours sicced an occultist on the Fantastic Four in one issue, mistaking them for witches.
- Tim Drake used his abilities as this to convince Batman that he should become the next Robin, though initially he was hoping to just convince Bruce that he needed a Robin after his downward spiral in the wake of Jason's death and didn't want the job for himself.
- Ultimate Spider-Man played with this. Peter's classmate, Kenny "Kong", was typically displayed as the dumb jock type. One day, while lying in his bedroom, he was able to put together the coincidences and realized Peter was Spidey. None of his classmates believed him.
- The Astro City story "Knight In Shining Armor" plays it very darkly with the character of Irene Merriweather (a Lois Lane Expy), who wants to expose the security identity of the superhero Atomicus so badly that she pulls off immense acts of Superdickery, like refusing to stop looking (and putting herself and other people in danger as entrapment bait) when the man she believes to be Atomicus (her own coworker) gets his house blown up by the Mafia because they got wind of her investigations. At the end of the story Atomicus is so fed up of her that he exposes his real identity, gives Irene a "The Reason You Suck" Speech, and leaves Earth forever.
- The Disney Mouse and Duck Comics have some superheroes... So of course there's people trying to find out their identities:
- Super Goof should be easy to figure out, given he's Goofy in long red underwear and blue cape... But as everyone is in denial, only his nephew Gilbert, his grandmother and Mickey know. Hilarity Ensues every time someone tries to find out, with the Beagle Boys once being more willing to believe Captain Hook was Super Goof rather than Goofy (later in that story, when a recently repaired supercomputer flat-out reveals that Goofy is Super Goof, they and O'Hara conclude it was still damaged from Super Goof's earlier sabotage, and they declare Tinkerbell as a more likely candidate).
- Paperinik's secret identity as Donald Duck is defended only by a Domino Mask... And his well-known abilities as a Master of Disguise who has openly disguised himself as Donald multiple times (indeed, an early story before said abilities became well known had the entire city sure he was Paperinik, at least until they saw a robotic Paperinik flying over them while Donald was in the open). Thus many a one-shot character tried to find out, with Gladstone and especially Scrooge joining the fun from time to time, only to be fooled by Paperinik's tricks (one of which had Paperinik being supposedly hit by radiations that temporarily gave him a beard impossible to shave-and Donald going out of his way to hide his chin just to have Scrooge take a fake bear from his face).
- In The Return of Hanuman, Munni noticed that Maruti looks rather different. The other gods were worried that she will expose Maruti's secret that he is actually Hanuman. Fortunately, she didn't even have the will to figure out what's wrong with Maruti.
- Dr. Kornbluth in Splash is intent on exposing Madison as a mermaid to boost his own career, although when he finally succeeds, he regrets his actions and undergoes a Heel–Face Turn.
- In the Richard Donner cut of Superman II, Lois Lane is this in spades, going even so far as to risk killing herself by jumping out a window and later pulling a gun on Clark and firing at him (she loaded the gun with blanks) just to prove that he is Superman.
- Inverted in Harry Potter. The Dursleys know full well that there's a whole world of magical people and creatures hidden from Muggles, and go to absurd lengths to try to pretend it doesn't exist.
- Robert Audley in Lady Audley's Secret goes to extreme lengths to prove the titular character's secret, as he figures out what it is fairly early on.
- Gladys Kravitz on Bewitched.
- Dr.Denman from H2O: Just Add Water, In the episode "Something Fishy", Cleo's sister Kim tries to prove that the girls are mermaids.
- To a certain degree, Dr. Bellows on I Dream of Jeannie, but more so his wife Amanda.
- Notably absent in Sabrina the Teenage Witch, much to the surprise of everyone.
- Until Brad showed up.
- Sergeant Doakes from Dexter.
- Detective Quinn becomes one as he starts to get suspicious about Dexter. However, he has secrets of his own and the closer he gets to the truth the less willing he is to pursue it further.
- Jack McGee from the TV show The Incredible Hulk.
- Elton Pope (and the rest of LINDA) from the Doctor Who episode "Love and Monsters".
- Eugene Jones from the Torchwood episode "Random Shoes" (after his death, Gwen ended up investigating him).
- One Monty Python's Flying Circus sketch takes this to extremes by having two women spy on their neighbours with high-tech surveillance equipment.
- In Pushing Daisies, Oscar Vibinius eventually ends up as one of these.
- Phil of the Future: Vice Principal Hackett is convinced that there is something odd about the Diffys. But he is only half right about them. He believes them to be space aliens, but they are actually from the future.
- Power Rangers:
- In the second season of Mighty Morphin' Power Rangers, Bulk and Skull became obsessed with discovering the Rangers' true identities.
- Cassidy and Devin in Power Rangers Dino Thunder were like this too (well, Cassidy chased the secret and dragged Devin along with her). They, like their predecessors, had no idea they were going to school with the heroes until the season finale, where they learn the truth and choose not to reveal it.
- Lois Lane in the Live-Action TV series The Adventures of Superman.
- In early seasons of Smallville, both Lex and Lionel Luthor suspect something is different about Clark, and go to great lenghts to try and discover it. Later on, in the episode "Hydro" Lois Lane attempts to prove Oliver Queen is Green Arrow. Oliver and Clark manage to convince her otherwise by having Clark dress up as the Green Arrow. In the episode "Identity" Oliver repays the favour by pretending to be the Red-Blue Blur when Jimmy Olsen suspects Clark Kent.
- The first season also had reporter Roger Nixon, who Lex hired to investigate Clark Kent.
- This is basically Vince and Dave's job in The Secret World of Alex Mack. When Dave finds out later on his own, he realizes that Danielle Atron and Vince are horrible people and becomes a Secret Secret-Keeper in relation to Alex.
- In Young Dracula, van Helsing is this to the Dracula family, following the imperative of his family line. Amusingly, he is a woodwork teacher.
- Fujimoto the sushi chef seems to be the only one who can see through Octodad's Paper-Thin Disguise.
- Bob Copper in Mega Man Star Force has this as, quite literally, his job description. When he's not trying to find out who Mega Man is, it's because the police force has tasked him to discover the roots of something weirder.
- Ivan Bezdomny from The Wotch, an intrepid (school) newspaper reporter who was dead set on finding the source of the 'Weirdness' surrounding Tandy Gardens.
- George from El Goonish Shive, a comicbook shop clerk who works alongside one of the main characters and was insistently badgering said main character to reveal the backstory of a magical incident that took place near the shop. That is until he abruptly dropped the subject after the main character revealed one of George's assumptions to be wrong and revealing to the audience that the reason for his badgering was to learn something that depended on the assumption being correct and that he didn't actually care for the backstory itself after all.
- Shin from Sailor Nothing — except that she succeeds and becomes a Sailor herself, and her analytical and research skills become a big asset to the other Sailors.
- Dib knows that Zim is an alien out to conquer Earth in Invader Zim. Unfortunately, despite constantly trying, he can't convince anybody else (except his sister Gaz, but she doesn't care).
- Denzel Crocker of The Fairly OddParents! is constantly out to prove the existence of FAIRY GODPARENTS!.
- Hans Rotwood from American Dragon: Jake Long. A teacher of the titular hero, he has an interest in supernatural creatures and is set on proving that Jake is one to the world once he has found out.
- Candace from Phineas and Ferb, the older sister of her two Child Prodigy brothers whose crazy inventions only she witnesses: by the time she fetches their mom, it always disappears by some crazy coincidence.
- Mandy from Totally Spies! has acted like this a few times, though the situation is usually solved by Laser-Guided Amnesia. She is the Alpha Bitch in the main characters' class who seeks to cross them wherever she can.
- Lt. Mitch Kellaway in The Mask movie and the animated series is both this and the Inspector Javert. (Not so much in the movie where Stanley does do illegal things with the mask, such as robbing a bank (he just happened to do so just in front of the goons).)
- Every Chicken Boo segment contains exactly one character who is aware that the titular character is in fact A CHICKEN I TELL YOU! A GIANT CHICKEN! This guy/girl tends to get ridiculed throughout the episode (or sometimes kicked out) until Boo's masquerade is stripped away somehow. If the wolf-crier was sent away, he/she returns at this point to say, "I told you he was a giant chicken."
- In the South Park episode "The Coon", Cartman spends most of the episode trying to find out who Mysterion is. He finally succeeds in having him unmasked when he convinces him that villains would continue to threaten the town unless he revealed himself. But the audience doesn't find out who it was until a later episode. It was Kenny and he is effectively immortal; waking up the next day after he dies and no one remembers his death. Also everyone figures that The Coon is just Bruce Vilanch.
- In Ultimate Spider-Man, Mary Jane Watson, aspiring journalist, seeks to discover Spider-Man's true identity.
- In Batman: The Animated Series, villainous scientist Hugo Strange uses a mind-reading device to find people's dark secrets and blackmail them. This leads to his discovery of Batman's identity, which he tries to sell to some of Batman's enemies.
- The Amazing World of Gumball Episode The Secret is dedicated to this trope. While they're locked in the bathroom, Gumball, thinking they're going to die, admits he's the one who drew a picture in Darwin's book that got him in trouble. Just as Darwin is about to reveal a secret of his own, they are set free. Gumball spends the entire episode trying to figure out Darwin's secret, eventually locking them in the bathroom again to get him to say it. It turns out that Darwin lied when he said a sandwich was great, because it was "just good." Gumball, understandably, is furious that the secret ended up being so trivial.
- It turns out that "secret" was a lie. The real secret was that he and Anais accidentally uploaded a clip of Gumball trying to hip-hop dance and destroying his room in the process.
- Roger a.k.a. 'Pink-Eye' from Grossology is obsessed with proving that Abby and Ty are Grossology agents and later with becoming one himself.
- Dipper Pines from Gravity Falls is obsessed with solving the mysteries of the titular town.
- Max Gibson in Batman Beyond was this in her first major appearance, trying to figure out Batman's identity just for fun. Later in the episode she switched her focus to identifying the Jokerz since they had been harassing her. Based on his frequent unexplained absences, his criminal record and other factors, Max incorrectly deduces that Terry (Batman) is one of the Jokerz. After sorting out that misunderstanding (and getting her life saved from the real bad guys), Max becomes a Secret Keeper.
- In Ready Jet Go!, Jet's next door neighbor Mitchell tries to find proof that the Propulsions are aliens.
- In the first season Mia and Me, Violetta seems to want to learn the secret of Mia's book, although by the second half of the season she seems to have lost interest. In the second half of the second season, she learns Mia's secret after obtaining a piece of the gem from her bracelet, which transports her to Centopia whenever Mia goes there.
- In Back at the Barnyard, Mrs. Beady is constantly trying to prove the existence of "talking barn animals".
- Atomic Puppet: Joey's nerdy classmate and nosy neighbor, Warren is determined to prove that Joey and his sock puppet Companion Cube are Atomic Puppet.