Retcon, short for retroactive continuity, is a literary term describing an intentional change to established events. Used mostly in comic books, retconning can also be found in long running television programs and film series. There are several varieties of common retcon changes that can help a new story work better or explain a past story with more clarity.
Some retcon changes add details to a previous story. For instance, a book may never mention whether the main character has a family; a later book with the same character may introduce family members. Addition retcon is often used when there is a blank period of many years in the character or world's background.
A less-frequently used form is called subtraction or rebooting. This form of retcon completely erases all previous stories about the character and starts over from page one. Although some of the same events may occur, they may be undertaken by different characters or for completely different reasons. The 2005 film Batman Begins is an example of a reboot, as the story for the previous films was thrown out and the origin of Batman completely rewritten.
One of the best examples for retcon that alters the story is found in Sir Arthur Conan Doyle's Sherlock Holmes series. At the end of the story "The Final Problem," Holmes is killed by his rival, plummeting off an enormous waterfall. Conan Doyle meant to leave the detective dead, but public outcry led him to continue the story. In "The Return of Sherlock Holmes," Holmes explains that he made it look as though he fell, but secretly he climbed up onto a ledge and hid before escaping. Alteration retcon is frequently used in soap operas, when long-dead characters occasionally show up with an amazing story of survival that often includes brain surgery, cosmetic surgery, desert islands and thugs of some kind.
Retcon is most often found in comic books, when many different authors write stories about a set cast of characters. Usually, sudden changes or alterations are explained by the character's having false memories implanted or losing his or her memory, or having past events turn out to be more than what they appeared. The first known use of the term retroactive continuity was in reference to a comic book, All Star Squadron #18 by DC Comics.
Drastically changing characters or established environments can occasionally lead to highly negative reactions by loyal fans, who suddenly discover a favorite character acting bizarrely and having a completely different past and life than was established. Retconning is dicey business with famous characters; while the writer may improve the story he is trying to tell, he runs the risk of destroying the connection a fan has with a character, thus losing sympathy. While it can be an excellent way to clarify a story or spruce up an old plot line, it can also be seen as disloyal to the spirit of the original.