The heroes need the help of a legendary figure who, over the years, has been idolized as the paragon of virtue, the source of all that is good and just, a true example for schoolchildren everywhere. The legend has beaten back all enemies, saved the day hundreds of times, and is truly a Knight in Shining Armor worth looking up to.
And then, when they finally meet this so-called legendary figure, they find out that he's anything but.
This is not to say that the legend didn't actually do all those amazing things people say he did. He's no Miles Gloriosus. The guy really is a hero. What he isn't, however, is a paragon of virtue. He's rude. He drinks. He smokes and is a bit of a womanizer and only got into the hero biz in the first place to make himself rich.
It's not the legend's fault that the heroes have idolized him. He can't control what other people say or think, after all. He, like the heroes, is only human, and the flaws that the heroes are complaining about are merely proof of their own unrealistic expectations. They had no right to expect him to match their daydreams. Exactly how serious the flaws are depends on where it lands on the Sliding Scale of Idealism Versus Cynicism; anything from minor foibles or even Good Is Not Nice to serious Anti-Hero territory is possible.
The trope name comes from Oliver Cromwell (1599-1658), who, in an attempt to avoid this trope, once told an artist to paint a portrait of him "warts and all". Official portraits were commonly done with the flaws in a person's appearance "corrected" by the artist. Cromwell wanted his picture to include his imperfections. Similarly, this trope is about the legendary character being finally seen for who and what he is, flaws and all. It is somewhat fitting that Cromwell, who the English idolize while still admitting to his flaws, is the Trope Namer.
Usually, this trope involves the lead characters convincing the legend that he must rise above his weaknesses and become the true shining example that they thought he was. A more Bittersweet Ending is possible if one of the leads gets caught up in the hero-worship and refuses to see through the foibles to the human being inside. Or worse, if they only realize the legend is human after a Heroic Sacrifice; if only the reader realizes it and the characters all refuse to, this trope can reach Tragic Hero heights.
An Aesop about expecting the Knight in Shining Armor is possible. Contrast Feet of Clay or No Hero to His Valet, where the "legendary hero" is anything but. Similar to Broken Pedestal, but there the characters have a rational grounds for thinking the legend is better than he is because they knew him when he was better. Inverse of Hero with Bad Publicity. A Historical Downgrade is doing this to a historical figure.
L/Ryuzaki in Death Note. Light mentions that most people would expect the #1 greatest detective in the world to be more detective-y. Instead, he's a barefoot young insomniac with a sweet tooth, non-existant social skills, and extremely poor posture.
In Vision of Escaflowne, Chid has a case of this toward Allen Schezar: his mother's tales of Allen's skill, bravery and heroism had led Chid to expect him to be an unbeatable hero. Allen showing up badly wounded and semi-conscious is something of a letdown to the boy, who'd been expecting someone rather more invincible.
Jiraya of Naruto is one of three legendary shinobi who have saved countless lives. Unfortunately for his apprentice Naruto, he's also a huge pervert who writes porn novels.
Played with in Fullmetal Alchemist, where the young Princess May Cheng has a sizable crush on famed alchemist Edward Elric - whom she's never met. She imagines him to be dashing, tall, and a complete bishounen with beautiful manners...then she meets the grumpy, snarky, vertically-challenged reality. It's done for laughs when she berates him for "toying with a maiden's affections" - and he stares at her and wonders who in the world she is.
In Mobile Suit Gundam SEED Astray, Kisato is a total fangirl of the legendary George Glenn, the original Coordinator and an Ace of the highest caliber. He ends up coming back to "life" when the team finds his Brain in a Jar and Professor hooks it into a hologram projector. However, he turns out to be a very goofy and playful fellow, which upsets Kisato's image of him as an austere, serene, larger-than-life figure. In the end, she accepts him after he convinces her that he's only human and legends always exaggerate...but she's still put off by how silly he is.
In Confession, Altar Boy learns that his mentor, the Confessor is a vampire — and Confessor refused to declare he had not killed people as a vampire. However, his Heroic Sacrifice not only won over Altar Boy, it inspired him to take up the mantle.
In Life in the Big City, an alien is put off by Crackerjack's arrogance, boasting, and foolishness, but follows him for a night and is almost persuaded not to send his race information they need to invade. Eventually he does it; not because Crackerjack is less than a hero but because other humans displease him.
For the last couple decades, it's been quite popular to portray Batman as a serious Jerkass, particularly to his friends and allies.
Booster Gold is a Large Ham who seems, at times, to be more interested in product endorsements, fame, and getting rich than he is fighting crime. Nevertheless, he really is a true blue hero who has regularly put his life on the line when the situation called for it. After the death of Ted Kord though, he became the hero he always wanted to be seen as. He has to constantly pretend to still be a greedy, shallow idiot so that he can effectively defend time. Sacrifice is a predominant theme in his new series.
The Warlord: This was the main theme of the 1992 miniseries, which largely consisted of the Warlord's friends and family telling the viewpoint character "Well, yes, he's a hero, but..." There's a fair amount of it in the current series, as well.
One issue of Jonah Hex is nostalgically narrated by a writer who, in the time frame the issue takes place, was a mute orphan. After his father dies, he runs into Hex, who saves him from being eaten by wolves. The two of them have some adventures (during which he constantly narrates about how awesome Hex is), he saves Hex's life, and then Hex leaves him to fend for himself in the Canadian wilderness.
Happens with the entire human race in the short Judge Dredd spinoff The Robot Hunter. A single robot, Smokey Joe, is sent to establish a massively roboticised infrastructure so the colonists arriving later will have a prebuilt utopia. Unfortunately Joe idolizes humans and makes sure every robot he builds know all about how awesome and fantastic the wonderful humans are. When the colonists show up, the robots see a bunch of soft and feeble fleshbags and not the living gods they were expecting. So they very reasonably decide that these are "simulated humans" sent as a test, and since their programming only apply to real ones, there's nothing stopping them from putting the lot in cages and doing horrible things to them. When their super-intelligent leader realizes their mistake and what they've done, his programming breaks so bad he regresses into childhood. Despite, uh, never actually having had one.
Lyze: Fancy it must be hard, meeting your hero and seeing that he's real and not a myth. Soren: You're just not— Lyze: Well what did you expect? Some Tyto alba with gleaming armor and battle claws, the moon rising behind him? (holds up his mangled talon) Well this is what it looks like when you've actually fought in battle. It's not glorious, it's not beautiful, it's not even heroic. It's merely doing what's right. And doing it again and again, even if someday you look like this.
Films — Live-Action
Hancock: Only one character manages to see through the appearance to heroism.
In Star Trek, Zefram Cochrane was the genius who gave the human race warp drive, thus taking the first step in the founding of The Federation. Star Trek: First Contact revealed that he was a cowardly, womanizing drunk whose intentions in building the first warp ship was "dollar signs, and lots of them".
Commander Riker: Someone once said "Don't try to be a great man. Just be a man, and let history make its own judgment." Zefram Cochrane: That's rhetorical nonsense. Who said that? Commander Riker: You did, ten years from now.
In Cat Ballou, Catherine is dismayed to find that Shelleen, whom she hired due to his high reputation with a gun, is constantly drunk and uncoordinated as a result. Even his horse shows a similar laid back attitude.
Schindler's List pointedly includes Schindler's womanizing along with his heroic actions.
Peter Jackson's 2005 version of King Kong has a good one. After Ann Darrow (Naomi Watts) is taken away by Kong, the crew goes off to rescue her, but about half-way (after a run in with some Raptors) Bruce Baxter, the intended star of Carl Denham's (Jack Black) film, decides to turn tail much to the disappointment of Adrian Brody's character. "I always knew you weren't the tough guy you played in the movies, Baxter, I just never figured you for a coward." Later on though, as Jack, Carl, and the rest are about to be killed, Baxter returns with the crew for a Big Damn Heroes moment and gets to be the action hero he always pretended to be.
The all-powerful Wizard of Oz turns out to be nothing more than a Snake Oil Salesman. His confidence trickster skills do, however, eventually save the day.
Malcolm X includes Malcolm X's early life as a criminal and the various controversies surrounding his life. It also finds time to remind the audience that Martin Luther King cheated on his wife. However, it ends with an anvilicious monologue about how Malcolm X was a great guy.
Sandy Mitchell's Ciaphas Cain is a Fake Ultimate Hero and among the most successful. Inquisitor Amberley Vail, his long-term associate and (apparently) lover, is perhaps the only person who can see past his sterling reputation. However, she herself thinks that he is too hard on himself, and possesses many heroic attributes. And she has a point. For all of his self-deprecation Cain does have a heroic side that shows through every so often, though he always quick to claim that he only saves people left, right, and center for strictly selfish reasons (the only one he fools is himself). Thing is, thanks to the unreliable narration from Cain's viewpoint, there's no way to be sure how much of Cain's heroism is really fake. Certainly, his handwaving to explain the selfish, cowardly reasons why he performed seemingly heroic acts looks rather thin at points. Assuming he is telling the truth about what he does, he's often actively trying to avoid danger and yet somehow ends up in it, so you can agree with his self-depreciation. On the other hand, more of the time he actively puts himself in harm's way even when there are numerous moments he could have quietly slipped away with no one the wiser and no harm to his reputation.
In Mitchel Scanlon's Warhammer 40,000Horus Heresy novel Descent of Angels, Zahariel's first glimpse of Brother Amadis disappoints him: merely a man, not a figure like Lion. But the longer he looks at him, the more he understands his character and heroism.
In Rick Riordan's The Battle for the Labyrinth, they meet up with Briares, the Hundred-Handed One, and find him demoralized and unwilling to fight, much to Tyson's distress. In the end, however, he does join in the final battle.
In Piers Anthony's Xanth, when the Gorgon asked Good Magician Humphrey to marry her, he set the same condition as anyone else who wanted an answer from him: she had to work for him for a year. When Dor discovers this, Humphrey explains that he feared this trope, because the Gorgon had thought herself in love after he cast the spell to keep her from turning people to stone. Working as his housekeeper for a year would ensure that she knew of all his little quirks and annoying traits before she married him — if she married him. A little later, the Gorgon explains to Dor that she had worked this out, and it is exactly what convinced her that he was the right man.
In Terry Pratchett's Unseen Academicals, Trev was bitter about his dead father. Nutt pointed out that his father had been only human, not a god; a good father; and, if perhaps a Fearless Fool who had gotten himself killed, yet people who had risked their lives had been important to the human race — an insight which profoundly moves Trev.
Discworld also references the Trope Namer in Feet of Clay when "Old Stoneface" Vimes, a Captain Ersatz of Cromwell, is persistently described as having 'warts and all' by historical romantics who essentially use this as their justification for considering him the bad guy (King Lorenzo, on the other side, was "extremely fond of children" but he looked the part).
The Wizard in The Wonderful Wizard of Oz, aka the Great and Powerful Oz. Less so in the book, where he is portrayed as a kindly old man who has simply gone astray in his balloon, as in the 1939 film, where he is shown as a Snake Oil Salesman.
John "Black Jack" Geary of The Lost Fleet. After being in suspended animation for over a century, he's found by a fleet on its way to a major offensive. He quickly discovers that he's nearly worshipped by people on his side of the war. This trope is a major theme of the series as a whole.
In Harry Potter and the Deathly Hallows, although Harry had known Dumbledore for over six years and saw him as a father figure, he realizes that he doesn't really know the true Dumbledore: what he does outside of school, what his history is, whether he's truly the paragon of virtue that Harry's viewed him as for years. That's what makes it all the more soul-crushing for Harry to read the (surprisingly true, considering the author) biography of Dumbledore written by Rita Skeeter, depicting a youthful Dumbledore championing Wizard superiority and being buddies with Grindelwald, who was effectively the Wizard Hitler. By the end of the book, Harry accepts that Dumbledore is not perfect, and that he is still the greatest wizard who ever lived regardless of how he used to be.
Poignantly subverted in Firefly. After arriving at a village that has put Jayne up as a folk hero due to a misunderstanding, Jayne eventually tries to make the townspeople understand he's just a regular guy, even going so far as to push over his own statue. They don't believe him.
Mal: It's not about you, Jayne. It's about what they need.
In Star Trek: Deep Space Nine, Dahar Master Kor is a legendary warrior that everyone gushes over. But he is really old and becoming more and more senile as time goes on. His legendary status gets stripped away when he starts reliving a battle from his glory days which gets a lot of his people unnecessarily killed. Shown for the senile old man that he was, the crew rejects him. But he redeems himself when he undertakes a suicide mission and shows that he still has the skills that made him the legendary figure in the first place.
In the Doctor Who episode "Father's Day", Rose meets up with her dead father, whom she knows only from her mother's stories. He proves to be up to his neck in get-rich-quick schemes and he and her mother quarrel almost continuously. However, in the end, her father makes a Heroic Sacrifice to save the universe. Rose's voice-over at the beginning and end of the episode are both about her father, but the concluding one is full of new insight.
Textbook demonstrated in an episode of M*A*S*H. Hawkeye's nightly habits catch up to him, and a hangover prevents him from finishing surgery on a patient. Radar, laid up due to an earlier injury, chastises Hawkeye for his failure, which results in his hero angrily yelling at him. After much discussion (and everyone in camp chewing out Hawkeye for his lost temper, Hawkeye included) Radar reaches the conclusion that he was human all along, and that seeing him off the pedestal, he might be able to like him more as a person than an idol.
Occurs in the Babylon 5 episode "Atonement". Delenn warns Lennier to stay on Babylon 5 when she goes to face the clan council, lest he find out about her biggest wart. He refuses because of his Undying Loyalty. When he finds out what it is - that she had cast the deciding vote for the Earth-Minbari war - Lennier tells her that he still has Undying Loyalty for her.
In Heroes, Hiro goes back in time to feudal Japan and meets his hero Takezo Kensei, who turns out to be a drunken Englishman. With Hiro's help, Kensei becomes the man the legends told of and discovers along the way that he's immortal and unkillable. A falling out between Hiro and Kensei turns Kensei into a villainous inversion of the man Hiro helped him become.
Guybrush ends up one of these in the eyes of fangirl Morgan Le Flay in the third episode of Tales of Monkey Island, though this is a big case of Wrong Genre Savvy on her part. She built up such an expectation of him as an unparalleled swashbuckler and unstoppable pirate that she never realized he was the protagonist of a comedic puzzle-adventure game.
The first, Solid Snake. He's been idealized as the legendary soldier who penetrated deep into enemy territory as part of FOXHOUND in two separate incidents to destroy nuclear weapons at great risk to himself. He's supposedly thought of in-universe as the modern James Bond, or such is the implication. Naturally, Meryl is surprised when Snake turns out to be rather coarse, rude and disdaining of her combat ability, as well as rather unhappy that he's involved in the mission to begin with.
Snake: The real me's no match for the legend, I'm afraid.
Mass Effect 3 plays with this by giving the players the decision of following this trope straight or not when Liara asks for input on a time capsule she's leaving for future generations to discover in case they fail to defeat the Reapers, with input that while hopefully allow them to succeed where they failed. Shepard has the option of letting Liara decided for herself how to comment on his/her work, painting them as a larger than life heroic figure, or not covering up his/her flaws and letting history decide for itself.
The game also does this with Javik, an ancient Prothean who was put into stasis 50,000 years ago and whom the player has the option of reviving. Liara, an archeologist who has spent her entire life studying Prothean artifacts and ruins, has built up an image of the entire Prothean race as a race of sages and scholars and diplomats. Reviving, and then interacting with, Javik reveals that the Protheans as a race were social Darwinist militaristic conquerors, and that Javik himself is a bit of a racist who holds all of the "primitives" surrounding him now in contempt. This latter attitude is somewhat understandable; when Javik went into stasis, humans and asari were still living in caves, and the salarians were swamp-dwelling animals who hadn't actually reached sapience yet.
This occurs to an extent during the Legacy DLC for Dragon Age II, which delves into the shady past of Hawke's father Malcolm. Though his past had been a mystery, Malcolm was by all accounts a good father who loved his family dearly and was even something of The Ace, being both a master mage and an excellent hand-to-hand combatant. During the DLC, Hawke (and their sibling, if still alive) discovers that Malcolm had never wanted a child with magic (he had at least one) and he was also a practicing blood mage who used his powers to imprison an ancient darkspawn mage named Corypheus. However, Hawke also learns he only used his Blood Magic to buy passage out of Kirkwall, and only because he was coerced by the Grey Wardens.
Rose of all people in Homestuck, from Kanaya's point of view.
Also, Dirk seems to have a very high opinion of Alpha!Dave. While he certainly was an amazing hero, he's far from flawless. And although we haven't seen it directly, the same is probably true for Roxy and Alpha!Rose as well.
In Hey Arnold!, Eugene is disillusioned when he learns that his idol is a foul tempered hypocrite. However, he's also a good person as demonstrated when he selflessly saves Eugene and Arnold from untimely deaths.
On Daria, an old sports hero comes to Lawndale High for a dedication, and everybody has to put up with what a Jerk Jock he is. The discrepancy between his honored status and caustic personality becomes even more difficult when he dies in an accident, evoking sympathy and Never Speak Ill of the Dead.
Often spoofed with Krusty the Clown in who is often smoking or doing other disturbing things which children might find shocking. He doesn't care about the kids, comedy or entertainment one bit; he's in it for the money.
A topic of the episode "Lisa the Iconoclast", in which Lisa discovers the town's founder, Jebediah Springfield, was actually a pirate who even tried to kill George Washington. Eventually she decides not to reveal this to the rest of the town, believing that his good image has always kept the town morale high and that it's better to keep the myth alive.