Believing Their Own Lies

""I reject your reality and substitute my own!""

- Adam Savage, quoting The Dungeonmaster

""It's no secret that a liar won't believe anyone else.""

- U2, The Fly.

A character, typically an antagonist, is known for for making some outrageous claims. Either vicious attacks against their foes, claims of divinity, or consistently twisting events so they look better.

In anyone else, these could be called out as Blatant Lies. But what sets this character apart is that, contrary to all evidence and the fact that they, by all rights, should know better, they honestly believe every word they're saying.

However sane they may have been when they started, they've gone over the deep end and are now Believing Their Own Lies.

Doublethink is an extreme example where the said liar does know better but keeps believing his own lies simply because he can. Sister Trope to A God Am I, where there is frequently overlap. The key difference is that this trope is less specific and doesn't have to be a claim of Godhood. This trope also applies only when the character should know perfectly well they aren't a god, but have convinced themselves otherwise.

See also Becoming the Mask, in which a character assumes a fake identity he ultimately wishes to keep. A Straw Hypocrite, who manipulates others by feigning to follow a cause, may get taken in by their own rhetoric this way. Compare Conspiracy Theorists, who think their outrageous claims are true from the get-go. With a little Obfuscating Stupidity, one can pretend to believe for as long as this gives an advantage.

Anime & Manga

 * God Eneru in One Piece had serious A God Am I issues. While knowing that, in the Sky Islands, "God" is merely a title for an island's leader, Eneru's Lightning-based Rumble-Rumble Fruit powers combined with the near-omnipotence granted by his enhanced mind-reading Mantra ability convinced him that he truly was divine.
 * Buggy the Clown; breaking a bunch of prisoners out of their cells in order to facilitate his escape from Impel Down caused him to start being referred to as "The Great Buggy-sama". This hit a critical mass when it emerged As a result, he started thinking he had a chance of taking Whitebeard's head. To put that in perspective, Buggy is on the low end of One Piece's Sorting Algorithm of Evil, and Whitebeard is called World's Strongest Man with zero exaggeration.
 * A villain of the week from the Yu-Gi-Oh! manga was a fake psychic (who physically made his prophecies of doom come true.) At the end, he's in a tight spot where only manifesting actual psychokinesis can save him, and he believes so hard he actually hallucinates that it's working.
 * The manga-only arc Onisarashi-hen from Higurashi no Naku Koro ni has Natsumi  In chapter 7,   Didn't you think

Comic Books

 * In an Archie Comics story, Veronica tells Archie and Reggie that whoever scores the most baskets in the next school game gets to take her out that weekend. Reggie attempts to sabotage Archie by telling him that the best way to improve his basket-shooting is to criticize himself constantly and harshly while practicing. This goes Reggie's way until Coach Clayton sets Archie straight, telling him that he should do the opposite while practicing and build up his confidence. Archie indeed goes on to score the most baskets, leading Reggie to wonder whether there was something to his "advice" after all. The story ends with Reggie practicing while berating himself and surrounding himself with demotivational posters.
 * Depending on the Writer, sometimes Lex Luthor actually believes that he is fighting to protect humanity from Superman. Other more minor villains, like (the most recent version of) Sam Lane, may believe the same.
 * Unknown Soldier from DC Comics, one of the versions. He is there when America liberates a Nazi concentration camp. He kind of snaps. Now he believes that whatever America does is right, no matter how horrible, because they once fought against the horrible Nazis.

Film

 * In the 1954 Biblical epic The Silver Chalice, Simon the Magician (Jack Palance) is a conman who gets rich by faking miracles. He convinces Caesar that he is able to fly, but eventually comes to believe in his own magic, jumps off a tower, and plummets to his death.

Literature

 * David Weber has done this in two of his series:
 * Cordelia Ransom, from Honor Harrington, is the head of the Office of Public Information for the People's Republic of Haven. She is the one who manages the PRH's propaganda, and in In Enemy Hands Citizen Admiral Thomas Theisman is horrified to realize that she seems to genuinely believe every word she broadcasts, and we see that her fellow heads of state are very concerned that Ransom believes her own propaganda.
 * The Masadans also believe things happened in a way that can't possible be true, all so that they can hold their women in less than slavery and continue to pursue their goal of destroying Grayson.
 * Also from David Weber are the "Archangels" of the Safehold series, especially Langhorne and Bedard. They set up a Path of Inspiration specifically to keep humanity from developing technology again, in violation of the original plans for their mission, in part to satisfy their own megalomania. Pei Kau-Yung grew concerned that they had actually come to believe they were angels.
 * And also from Safehold, this is, and is lampshaded as, the single creepiest attribute of church leader Zhaspahr Clyntahn—no matter what he does, he can come up with a justification for why it's the best course of action for everyone (and not just for him personally), often one that requires blatant disregard of facts he knows and doesn't know everyone else knows, and he seems to have compartmentalized his mind to such a degree that he can think himself innocent even as he knows he's guilty.
 * In the Kurt Vonnegut novel Cat's Cradle, Bokonon and Earl McCabe, rulers of the fictional West Indian country San Lorenzo, create a new religion, Bokononism, in order to improve their subjects' lives. To increase the new religion's appeal to the masses, McCabe outlaws its practice upon pain of death (while practicing it in secret), whereupon Bokonon "flees" into the jungle, a "wanted" man. Over time, however, the two men become so habituated to their respective roles in the charade that they go insane and become enemies for real.
 * Doublethink from Nineteen Eighty-Four, without which the entire system would collapse: The ability to consciously lie and tell propaganda, yet at the same time believe every word of it.
 * The Lord of the Rings: Gollum really believes that the ring was supposed to be his birthday gift.
 * Of course given that the ring, it's possible he can be excused.
 * A minor character in the Agatha Christie novel Cards On The Table. This led to an acquaintance of hers being part of Mr Shaitana's collection of uncaught murderers, because she'd convinced herself he'd killed for her.
 * Must be the case with Nozdryov in Dead Souls, who tells a lot of bullshit, even in court. You'll have to read it to see how much he BSs.
 * Because of their tendency to lose their old memories to The Fog of Ages, the Marra of The Madness Season who live for too long under a particular cover story eventually wind up believing it, to the point that they actually think that they are mortal and can die.

Live Action TV

 * The Goa'uld in Stargate SG-1. They're such Large Hams that it's impossible to believe they don't actually think they're gods. Ba'al and Anubis stand out, and have the advantage, by being savvy enough to remember they're not really gods.
 * An early episode, "The First Commandment," also featured the commander of an SGC team who fell into this trap himself and had to be put down by SG-1.
 * This is a possible interpretation of Sue Sylvester from Glee, seeing as how she keeps up the crazy claims even in her own diary.
 * Midsomer Murders has two guys running a spiritual center for years, only for one of them (the guru) to start believing in all his New Age-inspired nonsense, to the chagrin of his partner who wants to lead a different life.
 * One of the villains (a cult leader) from an episode of Law and Order Special Victims Unit started to believe his own hype and go a bit A God Am I. This caused his followers to turn on him.
 * When Kamen Rider Double's Detective Jinno was a beat cop, he had the effect of inducing this in others by being so gullible that the delinquents lying to him to get out of trouble would end up Believing Their Own Lies. It's a Crowning Moment of Funny when, after repeatedly distracting Jinno with claims of a UFO, a young Shoutarou eventually ended up searching for UFOs with him.
 * On Seinfeld George gives Jerry some advice on being a Consummate Liar with this little gem: "It's not a lie if you believe it."

Tabletop Games

 * The Balseraph demons from In Nomine essentially have this as the core aspect of their character. As fallen Angels of Truth, they become Demons of Deception, capable of weaving lies that others end up believing without question. But to do this, a Balseraph must first convince himself of the lie, warping his own personal truth to reflect the lie. For example, a Balseraph trying to convince a bar bouncer that he's a VIP must first convince himself that, "Yes, I'm a VIP, and I've been at this club dozens of times. Why isn't that bouncer letting me in already?"

Video Games

 * In the on-line game, War Of Legends, most of the Paladins honestly believe they are gods and that the game couldn't have been even thought of without them. Adding to the fact, they believe they won battles they clearly lost and make up excuses to avoid having to claim defeat while not letting others use the exact same excuses.
 * Metal Gear Solid V: The Phantom Pain reveals that mastered this trope to the point that not only does  believe the most blatant lie as fact despite all evidence to the contrary, but does it at a subconscious level;  lies and doublethinks so much  doesn't even realize  lying anymore.

Web Comics

 * This was one of the critical flaws of Order of the Stick's Miko Miyazaki. She was fundamentally incapable of seeing herself in the wrong, and would frequently convince herself of whatever she had to in order to keep it that way.
 * Additionally, Ian Starshine (Haley's father) raised his little girl in a Wretched Hive and taught her to lie at every opportunity whenever asked about herself. He's so paranoid he's incapable of taking people at their word and will invent elaborate scenarios which justify his ridiculous position and seems to totally believe them.

Western Animation

 * An episode of South Park involves Jimmy coming up with a gay fish joke. Cartman was lying on the couch the entire time and at first, he claims both he and Jimmy made it up together. Eventually he starts claiming he was the only one who wrote the joke while Jimmy was the one on the couch, and each time the story is told, he adds an increasingly outlandish event to it. It turns out he actually believes his lies.

Real Life

 * L. Ron Hubbard
 * Possible subversion? L-Ron himself never intended Scientology to be an actual religion. He wrote it as a science fiction novel. So this is a case of other people believing someone's lies.
 * He supposedly wrote it to win a bet with fellow sci-fi author Robert A. Heinlein, on whether a sci-fi writer could actually start a Cult of Personality around their works. Supposedly, Stranger in A Strange Land was Heinlein's attempt. The story goes that Heinlein backed off when he realized was that it was working, while Hubbard did not. The rumor dates from over a decade before the Manson Gang murders and People's Temple incident highlighted how abusive personality cults actually were, eventually leading to the discovery that the supposedly "good" personality cults of Stalin and Mao were actually much worse than propagandists made them seem at the time. There is no proof of the bet, though there are several witnesses who overheard their discussion (or claim to have). In any case, Hubbard himself quickly acclimated to his new role as cult leader, and many of Scientology's most successful practices (especially the "Attack the Attacker" policy that causes most of the controversy) were instituted on his explicit orders. Whether Hubbard ever came to actually believe in his own lies is debatable, but he certainly came to believe that profiting off the actions of the literal cult he created was perfectly ethical, regardless of the lives they destroyed in the process, as long as it remained legal.
 * Those Wacky Nazis. Which was part of the reason they were so... wacky.
 * To glue the new enemy to the old one, Nazi propaganda made up Josef Stalin's imaginary 3rd wife "Rosa Kaganovich". Apparently, they scattered a lot of propaganda leaflets for Red Army soldiers mentioning this particular bit of their Jewish conspiracy story. When Yakov Dzhugashvili was captured and interrogated they asked him about his father's private life, including this imaginary "last wife", which suggests they saw her as real. By some accounts, they even mistook Yakov himself for her son.
 * Unusual in that this particular fairy tale survived longer than its authors — after the war she eventually turned into either "secret wife", "Dr. Rosa Kaganovich Stalin" and even "mother" of Yeltsin's wife, or (in other branch, more responsive to the lack of evidence) Stalin's mistress. As the variations of this mythological character multiplied with time, now we have Roza Lasarevna/Moseevna/Mikhailovna Kaganovich, a sister/daughter/niece of Lasar Kaganovich, and/or also his personal doctor who poisoned him and became the cause for the last purge during his life, but at the same time vanished tracelessly. There was even a study How a Legend became a Woman: the Story of Rosa Kaganovich, Stalin's Secret Wife ("This presentation is dedicated to the problem of mythological versions of the biographies of political leaders" - you can find English abstract on the site of University of Helsinki).
 * Historian Ian Kershaw wrote extensively on the so-called "Hitler Myth", the Nazi propagated belief that Hitler was some kind of infallible genius and Germany's God-appointed saviour. As time went on and Hitler racked up achievement after achievement (rearming Germany, taking over Austria and Czechoslovakia, "solving" Germany's economic problems) that he started to believe it himself. Kershaw calls this moment "the beginning of the end for the Third Reich".
 * Using this makes for the most effective lies. A person will generally continue to exhibit "tells" as long as they continue to think of their lies as lies. Once you genuinely believe that your lies are true, your behavior will no longer suggest anything otherwise.
 * This belated punchline to the old "404 - WMD not found" joke.
 * Imperial Japan.
 * When the Pacific war against the Americans began to go south, the Japanese military from top to bottom began lying about inflicting losses to save face: increasingly disastrous defeats and ineffective attacks were rewritten as glorious victories and crushing defeats upon the Americans. The army often claimed fantastic victories (when they in fact had been defeated) and assigned their commanders ludicrious objectives based upon these assumptions, and the navy and the air force again and again claimed to have sunk entire American fleets, even when they had sunk no ships at all (certain American vessels, such as the Enterprise and the Essex were claimed to have been sunk multiple times). The Japanese high command, desperate to hold off the Americans, eagerly swallowed these lies and didn't bother to confirm them before informing the other branches of the service. This had disastrous consequences for all concerned; the army would often launch attacks and hold impossible positions because the navy blustered that the American fleet had been sunk, and vice versa. Japanese self-delusion was so effective that their defeat at end of the war came as a complete shock to much of the Japanese military and populace.
 * Korsakov's Syndrome. It's a form of amnesia brought on by excessive alcohol abuse. To cover up for their forgetting, patients will invent information that sounds highly plausible to everyone else and eventually come to believe it themselves.