Retroactive Legacy

Occasionally a company creates a fake 'legacy' for a character, and uses that as a basis for the character: Essentially a Retcon, introducing their past adventures into real life. By combining Retraux with Show Within a Show, the creators engineer a 'return' for a new character.

A specific form of Newer Than They Think. Some overlap with Absolutely Happened. See also The Gump for when the constructed legacy involves events "originally" performed by other characters. Compare and contrast Un Installment, where a single installment is "missing" from the midst of a series.

Anime & Manga

 * Kujibiki Unbalance (the first iteration) only had three episodes produced, spaced at random points along the nonexistant series. Despite that, there was a clip show back to episodes that never happened and next episode previews for episodes that also didn't happen.
 * The DVD bonus specials for Princess Lover! have episode previews for Magical Knight Maria-chan starring Silvie's kid sister. These include previews for episode 25 even though the first 24 don't exist, and previews for a sequel series.

Comic Books

 * The Sentry from Marvel Comics was a character "introduced in the '60s", and was so powerful that knowledge of his existence threatened the universe. So, he made everyone: even himself, even Marvel Comics, and even the readers forget he existed, until he "re"appeared in 2000.
 * Also from Marvel Comics we have Orson Randall, who wielded the power of the Immortal Iron Fist in the '20s, but passed into obscurity, completely unknown to the modern Iron Fist until he "re"appeared in 2007. The series also frequently delves into the histories of the Iron Fists that held the title before Orson, which go back for over a thousand years.
 * A side story even shows the Iron Fist from 1000 years in the future.
 * Similarly, recent Marvel comics have revealed that the Ghost Riders aren't the only Spirits of Vengeance. The British model draws from Spring-Heeled Jack, the German model closely resembles Shock-Headed Peter, and the Japanese one is a bosozoku with an oni-like appearance.
 * And there have been Spirits of Vengeance for every culture for every era; the American Spirits alone number in the dozens, and when the Vikings first landed in North America they found a Spirit of Vengeance protecting the shore.
 * A classic example from Marvel is Cable, who was created in the 1980s, but as soon as he was introduced he was written into history and characters acted like they had known him forever.
 * Marvel again: The series Alias introduced Jessica Jones, who had a backstory of being a C- or D-list superhero before retiring as a private detective. As with Cable, she's now treated as if she was active back in The Bronze Age of Comic Books -- and indeed Peter Parker's high school classmate in The Silver Age of Comic Books. Interestingly, the original plan was to have Alias feature an existing heroine, Spider-Woman.
 * The DCU had Triumph, a hero who was supposedly a founding member of the Justice League of America but a Heroic Sacrifice involving the timestream removed him from history and dumped him in the present day.
 * They did the exact same thing again with Moon Maiden, who was basically a cross between Sailor Moon and Superman.
 * Meanwhile, both DC and Marvel put up a lot of thought in the "retroactive continuity" in the Amalgam comics event, with fake creators, fake letters and fake notes from the editor for each book.
 * Alan Moore's first issue of Supreme was a tribute to the many versions of the character who had been published since his first appearance in the 1930s, all of which Moore had just made up.
 * Except Grim Dark Age Supreme, who was the original, Rob Liefeld version.
 * Alan Moore also wrote the Judgment Day mini-series for Awesome Comics. The series deals with a metacommentary of the notion of retcons to super-hero histories as Alan Moore himself creates a new backstory for the characters of Awesome Comics, to replace the shared universe they left when Rob Liefeld left Image several years earlier.
 * Greg Rucka's 2000s Checkmate series introduced a legacy character of the World War II heroine Mademoiselle Marie, and revealed that the original Marie was in fact just one in a long long of Maries dating back to at least the French Revolution.
 * Neil Gaiman's Sandman, Dream of the Endless, was introduced in the 1980s as the original from which the previous Sandmen had derived.
 * Grant Morrison introduced a new Shining Knight in Seven Soldiers, Sir Ystin, who heralded from the ur-Camelot that would establish the recurring cycle of Arthurian legend, and became the template for Sir Justin, the Shining Knight of a later era.
 * Happened to The Spectre in the John Ostrander series, who was given a history that stretched back into the Old Testament.
 * DC Comics occasionally assembles a legacy from previously-unrelated characters.
 * E.g., when a minor Golden Age Flash villain called "Rival" retroactively became the first Reverse Flash.
 * Or when Western heroes Nighthawk and Cinnamon became previous incarnations of Hawkman and Hawkgirl.
 * When James Robinson wrote Starman, DC had six characters by that name, only two of whom had any connection: Ted Knight; the 1950s Starman (who was actually Batman in a story that had been Retconned away); Mikaal Tomas; Prince Gavyn of Throneworld; Will Peyton; and Ted's son David Knight. Robinson created Ted's younger son Jack as "his" Starman, and forged connections between all the above characters, some of whom turned out to be the same people.
 * There was also the original Manhunter, who thanks to a retcon, first became a superhero after encountering the Manhunter androids (who in the real world had been introduced four decades after Kirk initally debuted). Later, it was established those androids took their name from the Manhunters from Mars, as seen in the pages of Martian Manhunter.
 * When DC licensed the Red Circle heroes from Archie Comics, they retroactively inserted the Hangman into DC's Golden Age during the 1940's. In his backup feature, it was established that Hangman had shared adventures with the Sandman.
 * Years after DC gained the characters Judomaster and Tiger thanks to a buy-out of Charlton Comics, the two were retconned into being members of the All-Star Squadron. Other retconned members of the team would include the Freedom Fighters and Plastic Man.
 * When the Milestone heroes were integrated into DC's continuity, it was established that Icon was now an old friend of Superman. It was also mentioned that Hardware knew Blue Beetle, and this throwaway line would later form the basis for an issue of The Brave and The Bold. Milestone Forever took this a step further, briefly showing a past team-up between Static and Wonder Woman.
 * The League of Extraordinary Gentlemen often features this, but the most obvious example is Campion Bond, who is introduced as a heretofore unknown ancestor of James Bond, demonstrating that careers are genetically transmitted in the LOEG-verse.
 * In story, this was what the military told the public Captain Atom was in his Post-Crisis series.
 * The Image Comics character Shadow Hawk named himself after the Silver Age Shadow Hawk, a parody of Silver Age Batman, whose teenaged son Squirrel would go on to become ShadowHawk's Evil Counterpart, Hawk's Shadow. Eventually it would be revealed that there was a line of ShadowHawks going back to Ancient Egypt.

Film

 * The first three Star Wars films began with Episode IV-VI, suggesting an epic series. It wasn't until much later that episodes I through III were created.
 * The first prints of Episode IV, however, did not have the "Episode IV" in the opening title crawl.
 * Leonard Part 6 supposedly followed five earlier adventures of the protagonist that had been suppressed in the interest of national security.
 * Toy Story 2 established Woody as a valuable antique cowboy doll who used to be the star of an old merchandise driven show called Woody's Roundup.
 * Plan 9 From Outer Space depicts the same alien race's ninth attempt to invade Earth.

Literature

 * The book The Princess Bride pretends to be an abridgement of an older book of the same name written by the fictitious author "S. Morgenstern". Remember those parts in the movie where they cut back to the grandpa reading the book to his grandson Fred Savage? William Goldman, the "writer" who abridged the book was read the book by his father, and equivalents to those scenes are present in the real life novel as footnotes and forewords.
 * The novelization of the 1984 movie The Adventures of Buckaroo Banzai Across the Eighth Dimension presents itself as merely the latest in a long series of "Buckaroo Banzai" books, and makes frequent reference to the titles and events of the alleged previous volumes, such as Bastardy Proved a Spur.
 * Trent's Last Case is actually the first novel featuring Philip Trent.

Music

 * Bruce Willis's The Return of Bruno was his debut album.
 * The Aquabats' first album was called Return of the Aquabats. They're that sort of band.

Video Games

 * D3 Publisher and Monolith's Eat Lead: The Return of Matt Hazard has been given an entire backstory of games (including that he was the "first character to crouch" although it was "removed at the last moment" before release of "The Adventures of Matt in Hazard Land" in 1983). They put up a blog about it, and a fake fansite complete with pointless animated gifs and one of those Java "lake reflection" headers.
 * Retro Game Challenge presents an entire alternate 1980s game industry, complete with magazines.
 * beatmania IIDX has a classical song called "Piano Concerto No. 1 'Anti-Ares'", supposedly written by one Virkato Wakhmaninov between 1893 and 1974. In actuality Virakato Wakhmaniov is a pseudonym of Jun Wakita, one of Konami's in-house composers, and he composed the song in 2004.
 * The DS game Dark Void Zero claims in its promotional material to be a game developed in the 80s by Capcom for a "revolutionary" yet ultimately scrapped arcade system with two screens. The game then eventually was used as the basis of the upcoming PC and console game Dark Void and thus Capcom has decided to "re-release" the "original" as a DS title.
 * The arcade system in question is a Playchoice-10, a Nintendo arcade machine with 10 different NES games inside it as the name suggests, and instead of lives/continues, feeding coins/tokens into it instead grants more playing time. And yes, it did have 2 screens, although since the games in question were NES games, the only purpose the second screen had was providing game hints and info. But after they released new info on the game, not only does the supposed backstory for the game contain tons of speculation, but the supposed promotional image for the game is blantantly photoshopped as well.
 * In Merry Gear Solid 2, the synopsis of the game Merry Gear is available in the Previous Operations section of the menu, and the plot is referenced in the game's story. The game never actually existed.

Western Animation

 * The Animaniacs episode "Back in Style."
 * The Animaniacs Warner Brothers and Warner Sister themselves, as well- they were old-timey cartoon characters locked up because they were too wacky.
 * Animaniacs character Slappy Squirrel was supposed to be a cranky old semi-retired cartoon character from Bugs Bunny's heyday. Why the Warners hadn't aged a day since their supposed debut in the 20s while Slappy had aged considerably since her supposed debut in the 40s ... um, clean living?
 * Because it's funnier that way.
 * It may also be a nod to a Tiny Toon Adventures episode exploring the nature of toons ala Roger Rabbit. It was an episode where Babs Bunny was seeking out old cartoon stars Bosco and Honey so they could be her mentors, and in the process learned that laughter is what keeps a toon young. The Slappy Squirrel episode "Critical Condition" suggests that no one has laughed at Slappy in a long time.
 * The second episode of Clerks the Animated Series was the locked-in-a-freezer clip show - they had trouble remembering, at first, anything that didn't happen the previous week, but eventually started talking about previous adventures they had.