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There are various motivations for applying retroactive continuity. The changes may occur to accommodate sequels or derivative works, allowing newer authors or creators to revise the diegetic (in-story) history to include a course of events that would not have been possible in the story's original continuity. Retcons allow for authors to reintroduce popular characters and resolve errors in chronology. Another form of retroactive continuity involves placing well-known characters in a parallel universe. This approach can be used to allow familiar elements of a story to be explored in an entirely new context, without affecting external elements. This approach can also be used to retcon former events in a franchise timeline.
Retcons are common in pulp fiction, and especially in comic books published by long-established publishers such as DC and Marvel. The long history of popular titles and the number of writers who contribute stories can often create situations that demand clarification or revision. Retcons also often appear in manga, soap operas, serial dramas, movie sequels, cartoons, professional wrestling angles, video games, radio series, and other forms of serial fiction.
The first published use of the phrase "retroactive continuity" is found in theologian E. Frank Tupper's 1973 book The Theology of Wolfhart Pannenberg:[page needed] "Pannenberg's conception of retroactive continuity ultimately means that history flows fundamentally from the future into the past, that the future is not basically a product of the past."
The first known printed use of "retroactive continuity" referring to the altering of history within a fictional work is in All-Star Squadron #18 (February 1983) from DC Comics. The series was set on DC's Earth-Two, an alternate universe in which Golden Age comic characters age in real time. All-Star Squadron was set during World War II on Earth-Two; as it was in the past of an alternate universe, all its events had repercussions on the contemporary continuity of the DC multiverse. Each issue changed the history of the fictional world in which it was set. 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, "Your matching of Golden Age comics history with new plotlines has been an artistic (and I hope financial!) success." Writer Roy Thomas responded, "we like to think that an enthusiastic ALL-STAR 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 then took firm root in the consciousness of fans of American superhero comics.
At some point, "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 18, 1990, Cugley posted a reply in which he identified himself as "the originator of the word retcon". Cugley used the neologism 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 previously were not part of the narrative and were not intended by earlier writers.
Retcons do not contradict previously established facts but instead fill in missing background details, usually to support current plot points. Thomas referred to "retroactive continuity" in this sense, as a purely additive process that did not undo any previous work; such additions were common in All-Star Squadron. Kurt Busiek took a similar approach with Untold Tales of Spider-Man, a series which told stories that specifically fit between issues of the original The Amazing Spider-Man series, sometimes explaining discontinuities between those earlier stories. John Byrne used a similar structure with X-Men: The Hidden Years. Possibly the earliest Marvel Comics example of new stories placed between long-established stories was the 1977-8 magazine The Rampaging Hulk. In The Godfather Part II, the character Frank Pentangeli is introduced as an old friend of the family though he is not referenced in the first movie; similarly Don Altobello is one of the "old time" Dons, though he is not mentioned until The Godfather Part III. Neither addition affects the plot line of the previous films. The addition, in later seasons, of an attic to the family's home in Full House stands as a similar additive example.
A similar concept is that of secret history, in which the events of a story occur within the bounds of already-established events (especially real-world ones), revealing different interpretations of the events. Some of Tim Powers's novels use secret history, 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 did not contradict or change any of the events depicted in the character's previous appearances, but instead changed the reader's interpretation of them. Such additions and reinterpretations are very common in Doctor Who.
Retcons sometimes add information that seemingly contradicts previous information. This frequently takes the form of a character who was shown to have died, but is later revealed to have somehow survived. This is a common practice in horror films, which may end with the death of a monster that goes on to appear in one or more sequels. The technique is so common in superhero comics that the term "comic book death" has been coined for it. An early example of this type of retcon is the return of Sherlock Holmes, whom writer Arthur Conan Doyle apparently killed off in "The Adventure of the Final Problem" in 1893,[page needed] only to bring him back, in large part because of readers' responses, with "The Adventure of the Empty House" in 1903.
In many of his detective novels, Rex Stout implies that his character Nero Wolfe was born in Montenegro, giving some details of his early life in the Balkans around World War I. But in 1939's Over My Dead Body, Wolfe tells an FBI agent that he was born in the United States. Stout revealed the reason for the change in a letter obtained by his authorized biographer, John McAleer: "In the original draft of Over My Dead Body Nero was a Montenegrin by birth, and it all fitted previous hints as to his background; but violent protests from The American Magazine, supported by Farrar & Rinehart, caused his cradle to be transported five thousand miles."
In the 1940s and 1950s, Isaac Asimov placed the planet Trantor, capital of the Galactic Empire, at the "center of the galaxy", but later astronomical research indicated that the actual Galactic Center might be occupied by a supermassive black hole, making human life there impossible; in later works, Asimov adjusted his galaxy and Trantor's location in it.
When E.E. "Doc" Smith wrote the original The Skylark of Space, space flight was a completely theoretical proposition. However, the last book of the series, Skylark DuQuesne, was written in 1963, when the United States and the Soviet Union were involved in the space race. Smith adjusted the past of his series accordingly, mentioning an American base and a Soviet one being established on the Moon prior to the protagonist Seaton discovering faster-than-light flight.
Retconning can bring back characters who were initially killed off. An example of this occurs on the CBS comedy Two and a Half Men. The character Charlie Harper (Charlie Sheen) was killed in a train accident in the ninth season, but in the season twelve series finale "Of Course He's Dead", it is revealed that Charlie survived the ordeal and has been held captive against his will for over four years. It is also common in soap operas. On The Bold and the Beautiful, Taylor Forrester (Hunter Tylo) was shown to flatline and have a funeral. When Tylo reprised the character in 2005, a retcon explained that Taylor had actually gone into a coma.
The TV series Dallas annulled its entire Season 9 as being just the dream of another character, Pam Ewing. Writers did this to offer a supposedly plausible reason for the major character of Bobby Ewing, who had died onscreen at the end of Season 8, to be still alive when actor Patrick Duffy wanted to return to the series. This season is sometimes referred to as the "Dream Season" and was referred to humorously in later TV series such as Family Guy.
Marvel Comics Beyonder was originally stated to be omnipotent and the most powerful being in Marvel Universe, coming from Beyond Realm. However, after his creator, Jim Shooter, left Marvel, writer-editor Tom DeFalco re-tooled the Beyonder, diminishing his power greatly: He was no longer omnipotent, as certain other cosmic entities were retroactively vastly upgraded to transcend the scale of infinity on which the character worked. Even after this, Beyonder was still one of the most powerful beings in Marvel, with several characters exceeding him.
In 2003, in the title of DC Comic's Teen Titans, Geoff Johns changed the entire genetic code of Kon-El the modern version of Superboy from a genetically altered human clone that was designed to be as Kryptonian as possible into a hybrid clone of both Superman and Lex Luthor. This change contradicted years of continuity and various facts that proved that Kon-El was human and in the process mostly ignored his unique ability of tactile telekinesis that made his powers very different from those of Superman.
Unpopular or embarrassing stories are sometimes later ignored by publishers, and effectively erased from a series's continuity. Later stories may contradict the previous ones or explicitly establish that they never happened. An unpopular retcon may itself be retconned away, as happened with John Byrne's Spider-Man: Chapter One.
Film sequels often employ temporal compression to maintain a sense of currency in each installment, despite more time having elapsed diegetically between one installment and another than has elapsed in the real world. For example, despite the implied contemporaneity in each of the films of The Omen series, the lead character ages some fifteen or twenty years across three films released across a period of less than six years.
Retroactive continuity is similar to, but not the same as, plot inconsistencies introduced accidentally or through lack of concern for continuity; retconning, by comparison, is done deliberately. For example, the ongoing continuity contradictions on episodic TV series such as The Simpsons (in which the timeline of the family's history must be continually shifted forward to explain them not getting any older) reflects intentionally lost continuity, not genuine retcons. However, in series with generally tight continuity, retcons are sometimes created after the fact to explain continuity errors, such was the case in The Flintstones, where Wilma Flintstone was mistakenly given two separate maiden names, "Pebble" and "Slaghoople", over the course of the series. Upon discovering the discrepancy, the producers settled on "Slaghoople" and retconned it into later series in the franchise.
Retconning is also generally distinct from replacing the actor who plays a part in an ongoing series, which is more commonly an example of loose continuity rather than retroactively changing past continuity. The different appearance of the character is either ignored (as was done with the characters of Darrin Stephens and Gladys Kravitz on the television series Bewitched, or Vivian on The Fresh Prince of Bel-Air), or explained within the series, such as with "regeneration" in Doctor Who, or the Oracle in The Matrix Revolutions. Sometimes, there are referential, inside jokes on actor changes in the show, such as with My Wife & Kids and Roseanne, where there was a change of actresses playing a role (characters Claire Kyle and Becky Conner, respectively). In the latter, another character observes that children can change as they reach adulthood, remarking that when Becky came back from college (played by a new actress), they couldn't even recognize her.
Retconning also differs from direct revision. For example, 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.
Retconning is not the same as a reboot or reimagining which completely discards the original timeline, such as in Battlestar Galactica. However, there have been partial reboots of franchises where the core of the franchise is still canonical but the expanded universe is relegated to a secondary continuity which, while not completely invalid, is subject to revision and critical review. Robotech is an example of this. With the release of the 2006 sequel film Robotech The Shadow Chronicles, Harmony Gold established that only the original 1985 animated series and the 2006 sequel film are considered canonical relegating the aborted Robotech II: The Sentinels, comics, and novels from the 80s and 90s to secondary continuity and, if elements are used from them, they are subject to selective revision and updating as appropriate to mesh with future canonical productions and to prevent conflict with the original animated series. While the Jack McKinney Robotech novel End of the Circle is evidently no longer canon, the prequel comic Robotech: Prelude to the Shadow Chronicles establishes that the general storyline of The Sentinels still occurred in some fashion, but various elements, including the timeline, specific unfolding of events, and some characterizations are different from what was previously depicted in earlier comics and novels. In such cases, the franchise producer may state that there is no intention to address the changes through remakes or direct retellings of such stories. It is essentially left to the viewer's imagination as to how differently the revised story unfolded.