Schwarzwald in The Big O. given the kind of world he's living in, he could very well be right
In Full Metal Panic, Mithril has programs that troll online forums and denounce anyone who makes connections about events Mithril was involved in as a conspiracy theorist so that nobody pays any attention to the (sometimes accurate) conclusions that the posters are coming to.
Teen Genius Susumu in Wandaba Style adamantly believes that the 1969 moon landing was fake, and is thus trying to get a rocket there himself (using environmentally safe methods). In the second half of the series, his mother is introduced as a Designated Villain, simply because she wants him to admit that he is wrong (it's her methods in doing so that put her into Villain territory).
In the IDW version of G.I. Joe, Mainframe came to be regarded as a conspiracy theorist after he stumbled onto the Cobra conspiracy. He went AWOL from the Joes and started living like a stereotypical conspiracy theorist as he attempted to prove he was right.
Cecil Holmes from PS238. Of course, in obsessing over the belief that his elementary school is a front for an alien invasion, he's completely missed out on its nature as a superhero training program.
Rorschach from Watchmen. He started as an Expy of The Question, who in the DCAU was a saner Expy of Rorschach.
In Twillight Sparkle's awesome adventure, ADMIRAL Awesome would rather believe that the President of Amarican is controlled by evil Martian deepsea fishes than that he would, of his own free will, refuse to give him any money or medals.
Mother: Did you know the Deputy Director of Planning was down in Managua, Nicaragua the day before the earthquake?
Crease: Now what are you saying, the C.I.A. caused the Managua earthquake?!
Mother: Well, I can't prove it, but...
Jerry Fletcher (Mel Gibson) from the movie Conspiracy Theory. By the end it hints that he was right about *all* his theories as the president gets caught in an earthquake just like he predicted.
The aptly named "Conspiracy Brother" from Undercover Brother thinks everything is out to get black people, and freaks out at even the most innocent-sounding of gestures. It takes real conspiracy theory skills to turn "Good morning!" into a two-minute paranoid manifesto.
Conspiracy Brother: Let me tell you something about the word "good," brotha. Good is an ancient Anglo-Saxon word, go-od, meanin' the absence of color. I.E. it's all good, which it is, OR Good Will Huntin', meanin, "I'm Huntin' Niggas!" So when you say good morning, what you're telling me is "I'm gonna kill yo black ass, first thing in the mornin'!"
At the start of the Stargate movie, Dr. Daniel Jackson is one. Specifically, he believes the pyramids were landing sites for alien spacecraft. The scientific community does not share his views and ridicule him. This is occasionally referenced in Stargate SG-1.
Of course, he was also right....
Though he doesn't believe that there's any kind of government cover-up, just that people got their facts wrong about when the Pyramids were built.
He believed that the fluoridation of drinking water in the 50s was a Communist plot to poison America. Believe it or not, this was an actual conspiracy theory at the time.
Reading between the lines, though, indicates that he came to this conclusion due to a sudden attack of impotence. So yes, the trope namer doomed the world because he couldn't comprehend that he was getting old and could no longer become erect at will.
Bobby Lee Swagger from Shooter. He has the 9/11 Commission report on his nightstand, and generally distrusts The Government (and for a reason). Nick Memphis also sees signs of conspiracy around the attempted presidential assassination where the president wasn't the real target, anyway, and gets tortured and almost "shoots himself" with the help of some Secret Agents.
In the '90s Disney Channel remake of the '60s comedy The Computer Wore Tennis Shoes, the main character's best friend was a stereotypical college-age radical who, in a parody of Kennedy assassination conspiracy theories, believed that President William McKinley was actually killed by his vice president, Theodore Roosevelt.
In the Film 8 Legged Freaks one of the Characters is a Conspiracy Theorist with his own radio station, which he uses to rant about aliens and the government.
Charlie's dad in So I Married an Axe Murderer is convinced that the world is run by a secret group known as "The Pentaverate:" the Queen, the Rothschilds, the Vatican, the Gettys, and Colonel Sanders "before he went tits-up."
In David Wingrove's Chung Kuo, Kim is a genius who in his teens uncovers the files showing the truth about world history, which has been falsified by the T'ang Lords
Luna Lovegood from the Harry Potter novels as well as her father Xenophilius Lovegood.
In the Night Huntress books, Timothy, Cat's next neighbor in the first book, is convinced the government covers up evidence of the supernatural (he's right). He later goes to work for "one of those magazines that give Cat's boss headaches".
Several flavors of this trope (alien abductee, Satanic cult victim, militia gun nut) appear in the Repairman Jack novel Conspiracies, which is actually set at a Conspiracy Theorist convention. Turns out the only genuine conspiracy there is an Eldritch Abomination plot targeting Jack himself.
Area 7 opens with an article from "The Conspiracy Theorist Monthly" (circulation: 157 copies) connecting a senator's death by hunting accident with the deaths of his wife and daughter by gas explosion. There's actually a bigger conspiracy going on than the writer knows...
Jonathan Shriek in Jeff VanderMeer's Shriek: An Afterword is perceived as one by the world at large because he insists that midgets who live underground secretly control the people in his home town with fungus spores. Of course everyone knows that there are midgets who live underground and really like mushrooms, but don't think that they're any more than that. They are wrong.
In Host, by Stephanie Meyer, conspiracy theorists were more likely to survive the Alien Invasion than the average person. This is because the aliens are Puppeteer Parasites and most people did not notice the difference, except the "crazies".
The Moon Is a Harsh Mistress included a conspiracy theorist as an aversion, as he disdains the conjecture that passes for 'theory'. Professor de la Paz pursued the study of historical conspiracies and developed a body of principles to describe how they work, how they fail to work, how they wind up being revealed. As a founding member of a revolutionary conspiracy, his theories are quite valuable for functioning in the scientific/academic meaning of the word. This also helps him develop his theory, since the most successful conspiracies are never revealed, the only way to be sure he's observing one is to take part in it.
"Haven't seen or heard a thing!" the Canadian replied. "I haven't even spotted the crew of this boat. By any chance, could they be electric too?" "Electric?" "Oh ye gods, I'm half tempted to believe it!"
In The Pale King, There's an old lady later revealed to be Toni Ware's grandmother who believes Jack Benny is attempting to achieve global thought control via radio waves. She covers her house with electrified hubcaps, which jams her neighbors' signals. She ends up getting cited for diverting her household's amperage, so she salvages a generator that runs on kerosene.
The Doctor WhoExpanded Universe contains a novel called Who Killed Kennedy which works as a Perspective Flip on the 1970s U.N.I.T stories by presenting it from the perspective of a journalist who becomes convinced that U.N.I.T and the Doctor are part of some malevolent organisation determined to uncover the truth, and ends up ruining his reputation and becoming considered one of these. It's partly Deconstructed; the general gist of what he believes is true, but he's got things completely wrong with regards to who are the good guys and who has malevolent intentions. He also learns that alien invasions are covered up mainly because no one would believe the truth.
In several of Tom Holt novels, recurring character (or possibly multiple characters with the same name) Danny Bennett is convinced that the Milk Marketing Board is somehow connected to the assassination of JFK.
Fox Mulder is a heroic conspiracy nut who is unusual both in almost always being right in his postulations about secret doings and in (usually) being a rational, shrewdly observant investigator who labors to find solid evidence to support his ideas rather than just relying on Wild Mass Guessing.
The Lone Gunmen are Agent Mulder's geeky friends and Conspiracy Theorists themselves. In their first episode, one of them tells Mulder that they like to hang out with him because his theories are way crazier than theirs.
The trio of conspiracy theorists from The X-Files, Langly, Bayers and Frohike got their own spin-off series The Lone Gunmen. Unfortunately, it was Too Good to Last. Ironically this has led to conspiracy theories about why it was canceled. Perhaps it was the March 2001 pilot being about an attempt by a shadowy government conspiracy to crash jet liners into the World Trade Center.
Hodgins on Bones. He takes it pretty hard when he misses the ancient conspiracy that has a member living in his house. Interestingly Hodgin's own family is wealthy and influential enough to features in the conspiracy he believes in. If anyone would know...
"You call it "conspiracy". I call it "the family business"."
Ron Reznick in "Nightshifter", who is convinced that the shapeshifter attacks he's been doing independent research on are caused by "mandroids".
In "Slash Fiction" paranoid whackjob Frank Devereaux doesn't put much stock in magic, but he's sure that "The government's been cloning people for years."
A downplayed example is Clive Finch from the Doctor Who episode "Rose",who despite sounding like an utter nutcase to anybody who doesn't know Doctor Who, he was mostly correct: he thought the pictures of the Doctor from various time periods were all the same man (they were), that the Doctor was an alien (he is), and that the Doctor is immortal (not 100% true, but 900 years is a hell of a long lifespan). The only thing he didn't guess was the time-travel angle.
Frank Lapidus on LOST, who believes the wreckage of flight 815 is a fake. He is of course correct.
There's also a hilarious conspiracy theory video in the season 4 DVD extras.
Star Trek: Voyager had an episode ("The Voyager Conspiracy") where Seven of Nine goes temporarily crazy from information overload and links most of the major events of the series up to that point into a massive Federation conspiracy to capture her, a Borg Drone... this is easily dismissed until you realize that, even though her conclusion about it being all about her was flawed and delusional, several of her premises were, in fact, quite grounded and made for some tantalizingly uncomfortable questions that were completely swept under the rug by the show... One can't help but wonder if there really WAS a conspiracy going on there...
Voyager was a long running highly episodic series with numerous writers of various qualities. As such, it included many plot holes, logical inconsistencies and cases of characters getting the Idiot Ball. This makes it a fertile ground for any theory that could go back re-explain past problems.
Leverage: "Wade Perkins" (Hardison) in "The Three Days of the Hunter Job", complete with a standard-issue Room Full of Crazy. Hilariously, Eliot and Hardison start telling Parker the stuff on there is real, just to mess with her.
His case was a rather amusing Deconstruction, as it turns out that all his beliefs were not only correct, but he knew the truth because he himself was an alien from another world who was suffering from a drug-induced [amnesia perpetrated by his fellow aliens.
Sam on The West Wing has recurring run-ins with a conspiracy theorist of the "there really were aliens at Roswell and the government is covering it up" variety. He got it from his father.
The hostage-taker from the Criminal Minds episode "Derailed" is one of the "the government is watching me" variety.
Field Commander Moss of Lexx is an over-the-top parody:
Moss: Take the 1 from 1600 Pennsylvania Avenue. Split it in half. Take the two halves. Now, attach them to the two zeros. What have you got? 666 Pennsylvania Avenue. Coincidence? I don't think so. There are no coincidences, my friends!
Mozzie, Neal's criminal contact, on White Collar, is incredibly paranoid and suspicious of the government, which leads to him acting out various Hollywood spy story cliches like meeting on park benches, playing loud music or running water during conversations, using code names, and so on. His antics are treated as ridiculous, but in the show's world, he may have a point.
Royal Canadian Air Farce had a recurring conspiracy theorist character who liked to share his theories with strangers on the street. According to him, the Kennedys were assassinated by Hitler, George W. Bush and Osama bin Laden are brothers, bin Laden is in Canada working at a gas station, and the Chernobyl accident happened because aliens spilled a Slurpee on the control panel.
In New Tricks, Brian Lane turns into one of these if he comes off his anti-depressants; most notably in one episode where the team are investigating the suspicious death of a prominent 1970s trade unionist, Brian — himself a member of the Police Union during his service — becomes convinced that he's being observed.
In the Law & Order episode "Absentia," a guru on trial for murder claims that the government is framing him ... and also that the government killed John Lennon.
Dudley Carew in the Midsomer Murders episode "Murder on St. Malley's Day". Amongst his theories was one that Lee Harvey Oswald was in Midsomer two weeks before Kennedy was assassinated.
The CSI: Crime Scene Investigation episode "Leapin' Lizards" involved a group of conspiracy theorists who believed that Earth's governments were controlled by a group of shape-shifting reptilian aliens.
Joe Garrelli from NewsRadio is obsessed with conspiracies, particularly ones involving the government's cover-ups of knowledge about extraterrestrials.
Angel. A god-like being who calls herself Jasmine has used her power to take over Los Angeles. Winifred Burkle, the only member of Team Angel to escape her influence, takes refuge in a conspiracy bookstore and asks the owner if he hasn't noticed anything strange about the way everyone is acting. The owner says that the CIA are still listening to the implants in his head, but it doesn't bother him any more as he's broadcasting Jasmine's love back to them via the mind control satellites. Jasmine later turns up at the bookstore, and grants the conspiracy theorist's greatest wish by telling him Who Shot JFK? — turns out it was Oswald.
In Supernatural, Dean and Sam come across several cases in a town where there have been kidnappings, light shows in the sky, and crop circles. They run into a group claiming it was aliens. Subverted when it is revealed at least one of the group is a Fairy, who is using the "alien" cover to make sure the Fair Folks kidnappings, light shows, and other effects are not taken seriously.
In Elementary, one of Sherlock Holmes' hobbies is to troll conspiracy theory websites and submit absurd theories that he makes up on the spot just to see what everyone else on the sites will believe.
"Everything You Know Is Wrong" by Chumbawamba is a parody of this trope.
Al, the bartender in Liberty Meadows, believes in numerous conspiracies, most notably that Shakespeare was actually written by Bacon.
The Deadlands supplement The Black Circle: Unholy Alliance had a Conspiracy Theorist archetype suitable for use as a player character.
In the collectible card game Illuminati, one of the groups you can control is the Conspiracy Theorists. They have zero Power (nobody believes them), but they let you hold an extra Plot card... because while they're completely wrong, they do have useful ideas. Another group, Paranoids, gives you protection against everything except Natural Disasters, because their worries are correct...
The Dark Mater Supplement for D20 Modern is also filled with conspiracy theories and just down right strange stories and information. Some of which is actually TRUE and caused this Troper to look up more than a theories presented.
Conspiracy theorists appear in Destroy All Humans!. In the first, they are referred to as "town crazies," and suburban ones are a bit more geared towards conspiracies than others (who are sometimes just plain nuts), even catching onto the plot of the Villain Protagonist. In the second, "The Freak," a California hippy, occasionally has these moments.
Pretty much every character in Deus Ex, but when one considers that the conspiracies usually prove true only minutes after being first mentioned, and that just one conspiracy is nowhere near enough for this game, it's to be expected.
Gomez, one of Deb of Night's regulars in Vampirethe Masquerade Bloodlines, comes up with increasingly bizarre conspiracy theories throughout the game... then in the final chapter, he suddenly starts citing the cosmology of the Old World of Darkness to the letter. The problem is: if that last "theory" actually precisely describes the very setting of the game, then what about the others?
A side quest in The Elder Scrolls IV Oblivion concerns a wood elf named Glarthir who is convinced that several people in town are involved in a conspiracy against him, and wants the player to help him find proof. He's wrong, but you can't convince him of it. If you try, he'll decide you're part of the plot, and try to dull his battleaxe on you.
If you investigate his house, there's lots of notes that indicate that he's been spying on them and the PC for a while. Also, from the second he first sees you in Skingrad, he follows you everywhere so there's no escaping his quest unless you run everywhere you go. He even follows you into the Mage's guild and your house, if you've bought the one in Skingrad.
Steven Heck of Alpha Protocol is a (supposed) CIA Agent/Psychopath who has knowledge of damn near every government conspiracy out there. He's actually right most of the time despite his insanity.
Otis Monday of Stubbs the Zombie, who mistakenly identifies a zombie invasion as a combined communist/Illuminati/New World Order/Nazi strike on his homeland.
In Dragon Age II, Cassandra (the Chantry Seeker interrogating Varric) is initially one due to her desperately seeking someone to blame for the Civil War. At first, she's convinced that Hawke and their companions planned the entire thing from the moment they set foot in Kirkwall. Deconstructed when we learn that there isn't a true Big Bad, and like in Real Life, most of the events are simply caused by a combination of coincidence and Grey and Gray Morality.
If Hawke aligns himself/herself with the Templars in the endgame Meredith also becomes this. A combination of her red lyrium sword's corrupting influence and her own Control Freak nature lead Meredith to believe that Hawke is the Big Bad behind Kirkwall's troubles (which of course makes her The Hero).
No-Bark is Novac's town crazy in Fallout New Vegas. He believes a rash of ghoul attacks coming from an abandoned rocket factory are the work of "Ghosts! Commie ghosts that don't know they're dead!" Their objective: to fly to the moon, paint it pink and stick Lenin's face on it.
Zeke is one of these in inFAMOUS. This clearly seen in his pad with Big Oil posters and often connecting something with a government conspiracy.
A minor example occurs in Pokémon Black 2 and White 2, if you play the male character. The trainer you meet at the Ferris Wheel during winter months (named Beauty December) tells you that "They" are out to get her because she has some secret that they want kept secret. She does battle you and ride the Ferris Wheel with you, but then warns you to stay away, saying "They" might get you too. (Of course, this could well be a subversion; there's no way of knowing whether she's paranoid or this is the truth.)
The Captain of the Gourd from Kingdom Of Loathing seems to think that tin cans, spiders, and/or goblins are conspiring against him and his precious gourd, and offers a side quest where he gives you a XP-granting item in exchange for can lids, spider webs, or Knob goblin fire crackers (depending on your main stat). According to the Captain's jar of psychoses zone, the Gourd whispers nonsensical conspiracy theories to him.
Homestuck: Roxy is considered one by her friends (mostly Jane) in-universe. Given that her theories include "Betty Crocker is an alien sea witch overlord", they're probably justified for having that opinion. Actually, she's got more or less the full story and is probably the only protaganist to get close to the full story behind BC.
And it turns out that this is because she lives hundreds of years in Jane's future, where the world was already conquered and ravaged by BC
In The Order of the Stick Miko made huge leaps in logic and crafted a huge conspiracy pinning the blame for a horrible situation that she created on Roy and company. It's ultimately the main reason she couldn't earn redemption — she just couldn't accept that anything was her fault.
Mr. Liatsis, a teacher from the V4 pregame of Survival of the Fittest, is commented on as being a notorious conspiracy theorist. Some students have their moments as well.
YouTube personality The Real Weekly News made a video called "Hulu Tube: Phasing You Out of YouTube." In this video, he states that the (at the time) recently added "Shows" tab on YouTube's front page was a grand conspiracy by companies like Burger King and Disney (seriously, those were his two big examples) to get all the normal content creators off of YouTube. Mentions of tin foil hats were pretty common from critics of the video.
Binder of Shame: Collateral Darren insists, among other things, that employers only insist on being sent resumes as part of a conspiracy to make more money for paper manufacturers, because at the interview you have to write down all the same information on a job application.
ATS has actually played a role in some notable conspiracy theories. Someone who called himself John Titor, posted on the site in 2000, claimed to have traveled back in time from 2036. His predictions of the USA falling to civil war and breaking into 5 subnations was memetic for a while, but disproven by 2004. Some of the first "no planes" 9/11 theories appeared on this site. Many ATS users suspected that the "no planes" theory was itself a conspiracy to make truthers proposing more rational theories look crazy by association.
Downplayed and lampshaded by The Nostalgia Critic when he believes the Spider-Man movies cut out a World Trade Center scene as to not offend anyone after 9/11.
Also, the tips at the end of shoelaces are called aglets. Their true purpose is SINISTER.
In his intro in the animation The Question's room aboard Watchtower is shown, with a posterboard showing an elaborate conspiracy that the Girl Scouts are behind crop circles, that the government is using boy bands to control the public, and that they are part of a single grand conspiracy with the aglets and the magic bullet. He's convinced that this all ties together somehow, but admits to not having figured out how.
In the same episode he comments that Supergirl eats peanut butter sandwiches. When asked if he goes through her garbage, he says one of his most memorable quotes, "Please... I go through everyone's trash."
Dale Gribble on King of the Hill. A believer in every conspiracy theory known, yet unable to discover that his wife had been cheating on him.
And when he finally realizes that the only time she could've gotten pregnant was during the time John Redcorn was visiting, he comes to the logical conclusion. His son was conceived when aliens artificially inseminated his wife!
Bart becomes one of these (and converts most of the other kids in Springfield) in The Simpsons episode "Grandpa vs. Sexual Inadequacy".
Matt Bluestone from Gargoyles, thanks to his obsession with the Illuminati (which actually does exist in the show's universe).
Members of "Humans Against The Extraterrestials" (from the second Teenage Mutant Ninja Turtles cartoon) believed that the aliens which had recently invaded Earth had left behind agents to infiltrate the planet, and were willing to blow up Manhattan in order to exterminate them.
Monkey: You don't trust anyone! Not even the mailman, and he's been coming here for thirty years.
Tigress: Planning something for thirty years!
Ron Stoppable from Kim Possible is like this at times. Many of his beliefs (such as the bad guys stealing Christmas and corn dogs) are proven incorrect. However, he has been right on a few occasions, such as claiming that the lake at Camp Wannaweep was dangerous or that Lord Monty Fiske (later known as Monkey Fist) was, as he put it, 'bad road'.
Kim:(elbowing Ron) Ron, that's Shego! Ron: Nah, it's not Shego, it's Miss Go — see, it says so on the board. Kim: Putting something on the board doesn't make it true! Ron: Oh, sure, y'know, when I said that in 20th Century History, I got sent to the office! Kim: The moon landing wasn't faked in the Arizona desert, Ron!
Dooper from Slacker Cats. He has a different theory each episode.