Retroactive continuity is the deliberate changing of previously established facts in a work of serial fiction. The change is informally referred to as a "retcon," and producing a retcon is called "retconning".
Retcons are common in comic books, especially those of large, long-established publishing houses such as Marvel Comics and DC Comics, because of the lengthy history of many series and the number of independent authors contributing to their development. Retconning also occurs in soap operas, movie sequels, professional wrestling, video games, radio series, series of novels, and any other type of episodic fiction. It is also used in roleplaying, when the game master feels it necessary to maintain consistency in the story or to fix significant mistakes that occurred during play, often under the synonymous (in this context) term "reality shift". Retconning also resembles the real-life occurrence of historical revisionism, where newly discovered information or a reinterpretation of existing information inspires the rewriting of histories.
In the letters column, a reader remarked that the comic "must make you [the creators] feel at times as if you're painting yourself into a corner," and that "Your matching of Golden-Age comics history with new plotlines [sic] has been an artistic (and I hope financial!) success." Writer Roy Thomas responded, "we like to think that an enthusiastic ALL-STAR [sic] booster at one of Adam Malin's Creation Conventions in San Diego came up with the best name for it a few months back: 'Retroactive Continuity.' Has kind of a ring to it, don't you think?" The term, possibly in limited use before All-Star Squadron #18, then took firm root in the consciousness of fans of American superhero comics.
"Retroactive continuity" was shortened to "retcon", reportedly by Damian Cugley in 1988 on USENET. Hard evidence of Cugley's abbreviation has yet to surface, though in a USENET posting on August 18th, 1990, Cugley posted a reply in which he identified himself as "The originator of the word 'retcon.' Cugley used the newly-shortened word to describe a development in the comic book Saga of the Swamp Thing, which reinterprets the events of the title character's origin by revealing facts that, up to that point, are not part of the narrative. In this case, the revelation is that the titular character's memories are false and he is not who he thinks he is. Alan Moore's retcons often involve false memories, for example Marvelman (aka Miracleman in America), and Batman: The Killing Joke.
Related to this is the concept of shadow history or secret history, in which the events of a story occur within the bounds of already-established events (especially real-world historical events), revealing a different interpretation of (or motivation for) the events. Some of Tim Powers novels are examples of this, such as Last Call, which suggests that Bugsy Siegel's actions were due to his being a modern-day Fisher King. Alan Moore's additional information about the Swamp Thing's origins didn't contradict or change any of the events depicted in the character's previous appearances, but changed the underlying interpretation of them. This verges on making alterations to past continuity. Such additions and reinterpretations are very common in Doctor Who, though they are not usually referred to as retcons by fans. The Star Trek books, The Rise and Fall of Khan Noonien Singh (Volumes 1 & 2), by Greg Cox, detail the fictional Eugenics Wars, giving alternate explanations for real world events such as the Indian nuclear test of 1974.
Additions are among the better-received types of retcons, because nothing is actually undone, and because people generally appreciate the explanation of [previously] ambiguous and/or mysterious events, although the changes to interpretation can still upset fans.
Hideo Kojima, creator of the Metal Gear Solid video game series, has likewise indicated his willingness to sacrifice continuity to a previous storyline--as with the date of Big Boss' loss of an eye (now in 1964 rather than the 80s). He also retconned Gray Fox's death in Metal Gear 2: Solid Snake and brought him back in Metal Gear Solid . On the other hand, many of these situations offer plausible explanations for how the character survived, by building on what we thought we saw, in which case they can be considered additions.
Fans may invent unofficial explanations for inconsistencies, the challenge itself becoming a source of entertainment. Sometimes these fan-made explanations become so popular and widespread that they slip into accepted canon, and the original creators of the characters accept them. An example of a fan-created retcon is in Star Wars. In the film, Return of the Jedi, it appears that the character Boba Fett suffers a horrible death in the belly of the Sarlacc along with many insignificant aliens. However, the Fett character was popular and few fans were pleased with his inglorious death. Popular casual speculation held that he had somehow escaped "off-screen" and later Star Wars books, graphic novels and even a Star Wars Unleashed action figure accepted this conjecture and depicted Boba Fett as having escaped the ordeal. How exactly Fett survived is not specified. In certain novels involving Boba Fett, he says that he detonated a bomb inside the belly of the Sarlacc, blowing him out of the stomach. It is important to note, however, that though George Lucas acknowledged that "some people think he survived anyway" when talking about the character in the commentary for the DVD version of the movie, he did not confirm or deny Fett's fate. However, in the commentary for the Special Edition Release, Lucas admitted that the beak was added to the Sarlacc and shown to devour Fett to make his death incontrovertible.
One of the most jarring retcons was in the TV series Dallas, where the character Bobby Ewing returned from the dead, after an absence of a complete season. This was explained by having his wife 'wake up' and see him in the shower, and realise she had dreamt the whole previous season. This left a mess of conflicting storylines and continuity issues within "Dallas," as well as conflict within the sister series "Knots Landing," which had a third Ewing brother, Gary, mourning Bobby prior to his brother's return, and the plot point was widely criticized as the moment Dallas "jumped the shark".
A lesser known example of an alteration retcon is in the film The Return of the Musketeers, based on Alexandre Dumas's Twenty Years After (Vingt ans après), his sequel to The Three Musketeers. In the film The Four Musketeers, Michael York, as D'Artagnan, presumably kills De Rochefort, played by Christopher Lee. However, in The Return of the Musketeers, both York and Lee turn up again, playing the same roles they had in the previous film, and it is explained that De Rochefort was seriously wounded, but not killed.
It is commonplace for fictional characters to remain the same age, or to age out of sync with real time; this can be considered an ongoing implicit retcon of their birthdate. When historical events are involved in their biography, overt retcons may be used to accommodate this; a character who served in the army during World War II might have his service record retconned to place him in the Korean War, the Vietnam War, the Gulf War, etc. This is similar to a problem faced by many works of future history: the events they describe happening in years after the initial publication do not conform to history as it actually happens. To accommodate such discrepancies, retcons may be used in later stories, altering dates or other details. An example of this can be found in the films Escape from New York and Escape from L.A. As well, a number of members of the G.I. Joe team are said to have served in an unnamed "Southeast Asian conflict" instead of in Vietnam, allowing the franchise to keep up to date.
While retconning is usually done without comment by the creators, DC Comics has on rare occasions promoted special events dedicated to revising the history of the DC Comics universe. The most important and well known such event was the mini-series Crisis on Infinite Earths; this allowed for wholesale revisions of their entire multiverse of characters. It has been argued that these were not true retcons, however, because the cause of the changes to their universe actually appeared within the story, similar to stories in which a time traveler goes to the past and changes history from how he remembered it.
In live-action television series, events in reality may force the creators to make changes. For example, in Star Trek: The Original Series, limits in budget and technology resulted in the appearance of Klingons as bronze-skinned, vaguely Oriental people. When the franchise was revived, the appearance of Klingons was changed drastically. The new appearance was explained by the producers to be how they always looked, but that they could not be portrayed as such before. The difference was noted in "Trials and Tribble-ations", an episode of Star Trek: Deep Space Nine, when modern-era characters travel back in time to the previous era, but dismissed by (modern) Klingon Worf as something Klingons "do not discuss with outsiders." This retcon itself was later retconned, in Star Trek: Enterprise, via a storyline in which it is revealed that the original, quasi-human appearance of the Klingons is due to a genetic mutation caused by an engineered virus.
Additionally, since the Space Shuttle Enterprise was named after the starship in the Star Trek universe, creators of the show have retconned actual history to claim that it was named after other historical ships of the same name.
Unpopular or embarrassing stories are sometimes later ignored by publishers, never referred to again, and effectively erased from a series' continuity. They may publish stories that contradict the previous story or explicitly establish that it "never happened", for example by claiming that events in a previous installation were "just a dream". Likewise, an unpopular retcon may even be re-retconned away, as happened with John Byrne's Spider-Man: Chapter One.
An example of subtraction can be found in Disney's The Lion King series. After the success of the first movie, Disney released a group of books titled The Lion King: Six New Adventures in which Simba is said to have a son named Kopa. It is also mentioned in the storybook version of the film that he has a son. However, in the film sequel The Lion King II: Simba's Pride, Simba only has a daughter named Kiara. Kopa is non-existent and no mention is made of him. Kiara also has a different coloring and more feminine features than the cub shown at the end of the first movie.
Retconning is also distinct from direct revision; when George Lucas re-edited the original Star Wars trilogy, he made changes directly to the source material, rather than introducing new source material that contradicted the contents of previous material. However, the later series of Star Wars prequels did qualify as "new source material", and many fans have pointed out instances that apparently retcon elements of the original trilogy.
The "clean slate" reinterpretation of characters - as in movie and television adaptations of books, or the reintroduction of many superheroes in the Silver Age of Comics - is similar to a reboot retcon, except that the previous versions are not explicitly or implicitly eliminated in the process. These are merely alternate or parallel reinterpretations such as the character re-interpretations of the DC animated universe or the Ultimate Marvel line of comics.
The animated series Frisky Dingo often gives previously unseen exposition in the "Previously on..." portion of the episode. (Not exactly Retroactive continuity because it only gives new information instead of changing already established events.) In addition to this, a brand-name "Ret-con" usually appears with products in these segments.
In the British science fiction television program Torchwood a drug used to erase the memory of characters is called "Retcon." Additionally, the use of the drug is often referred to characters as "retconning." This is a nod to the way retroactive continuity is used to preserve a story's continuity by erasing knowledge of events. Torchwood uses the drug to erase the memory of any given major plot event witnessed by any character other than one of the main protagonists, thus allowing for only the main characters to retain any information of such events. The nod to retroactive continuity is a joke meant to be shared between the writers and the viewers as a way of pointing out that anything done throughout the course of the series can easily be undone with a simple plot device, with a note to the fact that Torchwood's parent program, Doctor Who has made frequent use of retroactive continuity during its several decade run.
In Friendly Neighborhood Spider-Man, the Hobgoblin of the year 2211 carries a weapon known as a 'Retcon Bomb'; upon impact, it erases its target, and all memories of the target, from existence, though not erasing the consequences of their existence. This weapon has not been used since, because its inventor fell victim to one.
In the animated American comedy Family Guy's time travel-themed episode "Meet the Quagmires", Peter Griffin unwittingly assaults Ernie the Giant Chicken at a 1980s dance, retroactively providing Ernie with a grudge against Peter, and forming the basis for the continuing battle of "Peter vs. the Giant Chicken." Before this episode, it was believed that Ernie started the feud when he gave Peter an expired coupon. However, this episode proves that Peter--though unaware--does so instead, and the expired coupon serves as Ernie's revenge.