Walking Spoiler

A Walking Spoiler is Exactly What It Says on the Tin, a character or thing who has most of the tropes underneath it as spoilers. Sometimes, even its name is a spoiler, as it's so secret to the plot.

Can overlap with It Was His Sled, if the work in question is old enough that pretty much everybody already knows about the various plot twists.

Anime and Manga

 * This trope was inspired by The Idea of Evil from the Berserk series.
 * Danzo from Naruto is another good example.
 * Madara Uchiha from Naruto would also fit, since he is thought to be dead for a long time.
 * And then it turns out that he was dead, and the guy who's been pretending to be him all this time is someone else altogether.
 * Even Tsunade is one, since her becoming Fifth Hokage reveals that the Third Hokage, who resumed office after the death of the Fourth Hokage, is dead.
 * The Young Conductor from Baccano!. He seems to die early on, but actually is Claire Stanfield, an amazing assassin, The Ace and (Axe-) Crazy Awesome Sociopathic Hero. Hence he actually lived and becomes integral to the plot as The Rail Tracer, an urban legend that he created.
 * Hanyuu in Higurashi no Naku Koro ni is the real Oyashiro-sama, despises violence, and tries to change fate over and over, hence the reason for the repeating worlds. In the anime, they censored out Rika's screams to Hanyuu as Hanyuu stabbed herself in front of Rika and Shion, and made you believe that only those who heard Hanyuu were crazy (Rena, Keiichi, etc.), or else too high up on the Hinamizawa Syndrome scale.
 * In Umineko no Naku Koro ni, several characters are walking spoilers: EVA-Beatrice, Magician Battler, and Beatrice Castiglione.
 * In Tsubasa Reservoir Chronicle, the fact that the Syaoran who is the protagonist of the story is really a clone of the original who is sealed away in a glass cage by the villain is a well-done plot twist.
 * King Bradley/Wrath from Fullmetal Alchemist. His "son", Selim Bradley/Pride even more-so, though it's nicely handled on the character page by listing them as separate characters on separate pages, though Pride is pretty much an all-white entry as a result.
 * Also, Father -looks like an old Hohenheim clone while Hohenheim's appearance is a spoiler, is the actual Big Bad behind a giant conspiracy.
 * In the 2003 Fullmetal Alchemist anime, Pride and Big Bad Dante are examples.
 * In Puella Magi Madoka Magica, the catalyst that starts the true story is the death of Mami Tomoe by sudden and violent decapitation. Since the story does a complete 180 at this exact moment, it makes describing Madoka's actual story to someone very difficult without pointing out that an important character is mercilessly killed.
 * Risa Kamizaki and Mika Makihara from Amagami both are responsible for that rejection. The former tricks the latter thus causing Junichi to think he was stood..
 * Mello and Near from Death Note; the fact they're L's successors (coupled with L's utter refusal to give up on the Kira case) are an easy tip-off to the fact that L dies.
 * In One Piece, it's difficult to talk about the four Cipher Pol agents undercover in Water 7, especially not Kaku and Lucci, without revealing their being The Mole. Similarly, discussing Vivi typically reveals that she's undercover in Baroque Works as Ms. Wednesday. And then there's Kanjuro, introduced in the Dressrosa arc as seemingly a friend of the samurai Kin'emon and the ninja Raizo, but at the beginning of the third act of the Wano arc is revealed as an undercover agent for the arc's secondary villain, Orochi.
 * The Character page for G Gundam spoilers out every last entry (and the name) for Ulube Ishikawa, due to him being revealed as the Big Bad about, oh, four episodes from the end.
 * Nia in Tengen Toppa Gurren Lagann: is the Spiral King's daughter, appears after Kamina's death.
 * Zeref from Fairy Tail. Even the fact that he's alive at all is a spoiler; this combined with him being quite different then how he had been originally described makes it essentially impossible to mention him to someone who hasn't read up to the point where he appears without spoiling something.

Comic Books

 * It's pretty much impossible to discuss Invincible without spoiling that Omni-Man, the protagonist's father, isn't a Superman Expy so much as a villainous advance scout for a race of alien conquerors.
 * Just try to explain the original concept of Thunderbolts without revealing the twist.
 * Trying to discuss Ozymandias of Watchmen in much detail beyond his being a resourceful rich and powerful person is difficult without spoiling not only that he's the hidden mastermind behind much of the events of the series, but his motive for doing so.

Fan Works

 * The Katawa Shoujo fic Reconciliation has an interesting variant in a character whose conspicuous absence serves as a Walking Spoiler. It's revealed early on that Hisao has died of a heart attack, setting the plot into motion. Only the most basic description of the setting can avoid mentioning his death.
 * Ekaj in Naruto Veangance Revelaitons is Ronan's son, and it's almost impossible to talk about him without mentioning this relationship.

Film

 * Harry Lime from The Third Man is also a possible example, because throughout most of the movie he's thought to be dead.
 * Axelrod from Cars 2.
 * Thanos from the first stinger for The Avengers.
 * Kylo Ren from Star Wars: The Force Awakens. Everything about him other than the fact that he's an obvious Darth Vader wannabe is a major spoiler.
 * Hans from Frozen. He's one of two potential love interests for Anna, but then...
 * Bellwether, the Deputy Mayor of Zootopia who initially is Judy Hopps' influential friend in high places. But then it turns out she has a much different role in the events of the movie than we were initially led to believe.
 * King Candy in Wreck-It Ralph is this to some extent, with his true identity being a plot twist.
 * Boingo, the bunny from Hoodwinked. At first, he seems to be a chatty friend of Red's, but then he shows up in strange other contexts as the other characters tell their version of the day's events. It's difficult to discuss him in detail without revealing the main mystery in the film. Like Sirius Black and Peter Pettigrew of Harry Potter, he reappears in the sequel and it's assumed viewers already know the twist.

Literature

 * The Dresden Files is a classic example. It's really hard to talk about the series without spoiling something. One of the biggest examples is Molly Carpenter, Michael's oldest daughter, who has magical talent and becomes Harry's apprentice.
 * A Song of Ice and Fire is such an extreme example of this, it is impossible to give a one sentence plot overview of the series without giving one and a half spoilers as one has to say that the king dies and for various reasons he doesn't have a direct heir
 * The Steerswoman books are actually relatively hard science fiction novels about a Lost Colony, not fantasy.
 * In The Gone-Away World, the hero doesn't actually exist until about halfway through the book—before that, he's a figment of his best friend's imagination.
 * The last Mistborn book is a bit tricky to describe without giving away that a) the real Big Bad is the god of destruction, Ruin, and b) at the end of the first book, Marsh was turned into a Steel Inquisitor, which is now allowing Ruin to use him as a puppet.
 * From the same author, you can't really talk about the second half of Warbreaker without revealing that God King Susebron is a perfectly harmless figurehead rather than an Evil Overlord andBluefingers and Denth are not allies of the protagonists but the Big Bad and his Dragon with an Agenda respectively.
 * Rock and Hollyleaf from Warrior Cats. Rock because he's God and Hollyleaf because of how dynamic her character is.
 * Sirius Black and Peter Pettigrew from Harry Potter. There is no way to give an accurate description, however brief, of either character without spoiling The Reveal at the end of Harry Potter. In subsequent books, both appear on a recurring basis with their true natures taken for granted.
 * Welstiel in the Noble Dead series of books by Barb and J.C. Hendee is a man of mystery in the first book, Dhampir. Starting from the second book and continuing into the third, we discover his true nature, his backstory and relation to the protagonist Magiere, and his goals.

Live Action TV

 * River Song from Doctor Who. This even applies in the series - thanks to time travel shenanigans, her timeline runs in the opposite direction of the Doctor's, so her "earlier" is his (and the viewers') "later." Her catchphrase literally is "Spoilers!"

Video Games

 * Purple Eyes from Pokemon Ranger: Guardian Signs. He comes in after the Not So Fast Bucko ending as the new leader, and directly leads into the next villain.
 * In Dragon Age Origins, every mention of major villain Teyrn Loghain Mac Tir as a possible Player Party member is always covered in spoiler tags because the very fact that he can become one is a major plot twist. When that is not possible, he is conventionally referred to as "Secret Companion".
 * The infamous Hidden Fun Stuff from Dwarf Fortress. It's an Unusual Euphemism for Hell and its resident horde of demons, which will invade your fortress if you dig too deep.
 * The 16th playable character in The Reconstruction, Tezkhra, is first heard of as the god worshiped by certain groups of shra.
 * Darkrai from the second set of Pokémon Mystery Dungeon games is an example of a Man Behind the Man who appears after you think the story is over.
 * Mass Effect has several examples of this
 * The revelation that Sovereign from the first game is the true Big Bad is treated as extremely sensitive. The Reapers in general are not considered spoiler information, but he is.
 * Legion from Mass Effect 2 doesn't join you until the endgame, and the fact that he/it/they even can be a protagonist is a twist, causing him to be a major source of spoiler tags.
 * Morinth from the same game. You can recruit her in place of her mother, Samara, if you choose to betray the latter during the climax of her loyalty mission. Even the fact that the Ardat-Yakshi is Samara's daughter is a twist.
 * The Human Reaper from the same game is the final boss, and the entire Collector plot revolves around it.
 * Javik in Mass Effect 3, since his very existence spoils the fact that not all the Protheans are dead, since the first game had the few survivors' life pods run out of power while on Ilos, and by the time Shepard and company reach it they've all been powered down. Also ties into The Reveal in Mass Effect 2 that the Collectors are actually indoctrinated Protheans.
 * The Catalyst from the same game, since he literally only appears in the last scene of the game.
 * Damn near every character in Xenoblade except for maybe Reyn and Riki, although Fiora is by far the most obvious one considering she was implied to have died a few hours in but got turned into a Robot Girl instead.
 * But most especially Zanza, who seemed to be a semi-important character introduced and swiftly killed off at the end of the Prison Island storyline. Turns out that technically wasn't even him, and not only is he the Final Boss, but one of the two gods of the world and the Monado itself!
 * Wheatley turning out to be an antagonist in Portal 2 is meant to be a big twist. Thus, spoilers. Everywhere.
 * In BlazBlue Saya appears to be Ragna and Jin's Dead Little Sister. Turns out that she's actually The Man Behind the Man (although it's not made clear if she's just serving as Terumi's puppet and it's implied that she's possessed or otherwise Not Herself)
 * The mild-mannered pacifist Captain Hazama was one himself until the trailers for Continuum Shift outed his secret.
 * Mu-12 was one as well, until the Continuum Shift II trailer casually showed Noel transforming into her.
 * Yomiel, the mysterious Big Bad of Ghost Trick. When he shows up, the game pretty much heads into one Mind Screw and Plot Twist after another.
 * Clayface in Batman: Arkham City. Along with a few characters in sidequests.
 * June and Ace from Nine Hours, Nine Persons, Nine Doors, as both turn out to be the primary antagonists (and the true protagonist in June's case) in roundabout ways.
 * Joshua, and, to a lesser extent, Hanekoma in The World Ends With You. Kitaniji too, as you don't really learn his real role in the plot until the very end.
 * A few Kirby villains can fall under this trope, such as Magolor from Return to Dream Land and Marx from Milky Way Wishes.
 * Normally, Kor from Jak II Renegade would just be your typical old man. Most of his tropes come from the fact that he's really the Metal Head Leader in disguise.
 * Then the reveal that Jak and Samos are originally from the future and the time machine they found in the past was infact the same one made by Kira at the end of the game that was supposed to bring them back.
 * The fact that Revan is the Player Character of Knights of the Old Republic is a major plot twist, causing the former Dark Lord of the Sith become the main source of spoilers of the game. This makes the first sentence of the plot synopsis for the game on Wookieepedia (unless it has been changed by the time you read this) a huge spoiler for The Reveal more than halfway down the plot.
 * After you defeat Medusa in Kid Icarus: Uprising and the fake credits roll, The true Villain, Hades, comes in and takes over the Underworld Army. And since we were build up to believe that Medusa was the Villain with no hints of Hades being in the game...
 * To a lesser extent, pretty much everyone who is introduced after Chapter 9, which is built to look as much like the final dungeon as possible.
 * In the Ace Attorney series, on this wiki, the more spoiler tags that are on a character's entry in the character sheet, the more likely they are to be a murderer. Each of the games' main antagonists count.
 * The Golden Spider/Chakravartin from Asura's Wrath with only one trope unspoilered it is quite evident that he is a major character later on.
 * Forrest Kaysen from Deadly Premonition. Many spoilers are required to conceal that the fat, jolly tree salesman is not only the Big Bad of the game, but a Complete Monster Humanoid Abomination to boot.
 * About two-thirds of the way through Final Fantasy V, the party meets Krile. She is a friendly young girl. This is the most detail you can describe her with if you don't want to reveal that she is Galuf's granddaughter, a princess (because he is really a king), or that she takes his place upon his death.
 * Lion and Will's first appearance in Umineko no Naku Koro ni is in the seventh episode of the sound novel.
 * The Binding of Isaac takes the cake with five different examples, primarily due to the abundance of bonus levels. The first two, Mom's Heart and It Lives, are mostly out of this territory since their section of the dungeon is almost immediately unlocked. Satan, secret boss of Sheol, is considerably more of a spoiler, but probably more well-known since the Halloween update has been out for a while. The biggest ones are Isaac himself as the standard final boss of The Cathedral, and Daddy Long Legs II/The Tri-Achnid as the ultimate super-secret final boss. (For now, anyway.)
 * Non-character example, the Keyblade in Kingdom Hearts. Trying to explain what this weapon is and what it's for would likely spoil about 20 games in the franchise, so if you're new to said franchise, it's best not to get into it.
 * In Undertale, there are Asriel Dreemurr and the Fallen Child. We learn about their existence near the end of the neutral route, and they play a role in the Good and the Genocide Routes.
 * Five Nights at Freddy's is one of the most Spoilered Rotten game franchises ever made, and any discussion about the past and motivations of any character is likely to give something away.

Webcomics

 * Diva'ratrika Val'Sharen, Liriel and "Diva" from Drowtales due to the fact that they are all technically the same person, with the last one being the final result of a Fusion Dance of the Diva'ratrika with a servant, with Liriel being the incomplete fusion. All of which spoils the fact that Diva'ratrika has been dead since nearly the start of the story, with the coup that eventually killed her occurring in the story's prologue.
 * And most things about Kalki Nidraa'chal from the same series also qualify. While she actually appears in the Prologue of the story, it takes 25 chapters for us to find out what her deal is. And while quite a few people had already guessed that she was really Snadhya'rune Vel'Sharen's daughter, even with a Shrug of God that while she was Snadhya's daughter Snadhya had never given birth, chapter 25 was a Wham! Episode in that the explanation of how this was possible also revealed other gigantic spoilers: Mainly, that the Val'Jaal'darya have not only figured out how to carry a child outside of the mother's womb, but also make a child have two mothers. And Kalki's second mom? None other than Mel'arnach Val'Sarghress, the protagonist Ariel's real mother, which basically makes Kalki related to half of the important cast members in some form or another. Whew.
 * In Homestuck Doc Scratch is a near-omniscient being who's the First Guardian of the trolls' universe, while it was somewhat of a late revelation that the trolls live on another planet. Scratch is also the precursor to Lord English, a mobster who turns out to be one of the three BigBads... or something.

Western Animation

 * Queen Chrysalis and the Changelings, from My Little Pony Friendship Is Magic. Their very appearance is a spoiler, as promotional material for the season 2 finale made the episode seem to be about wedding hijinks.
 * Hiroshi Sato in The Legend of Korra, whose part in the Seventh-Episode Twist turns his entire characterization on its ear.
 * Breakdown in Transformers Prime, whose death and implied rebirth as Silas' new body have seemingly caused Hasbro to delay and deny the existence of his toy.
 * Shockwave in Transformers Animated, right down to him being Shockwave, as he was undercover as the Autobot Longarm.