Sequel

A sequel is a work of literature, film, theatre, television, music or video game that continues the story of, or expands upon, some earlier work. In the common context of a narrative work of fiction, a sequel portrays events set in the same fictional universe as an earlier work, usually chronologically following the events of that work.
In many cases, the sequel continues elements of the original story, often with the same characters and settings. A sequel can lead to a series, in which key elements appear repeatedly. Although the difference between more than one sequel and a series is somewhat arbitrary, it is clear that some media franchises have enough sequels to become a series, whether originally planned as such or not.
Sequels are attractive to creators and to publishers because there is less risk involved in returning to a story with known popularity rather than developing new and untested characters and settings. Audiences are sometimes eager for more stories about popular characters or settings, making the production of sequels financially appealing.
In movies, sequels are very common. There are many name formats for sequels. Sometimes, they either have unrelated titles or have a letter added on the end. More commonly, they have numbers at the end or have added words on the end. It is also common for a sequel to have a variation of the original title or have a subtitle. In the 1930s, many musical sequels had the year included in the title. Sometimes sequels are released with different titles in different countries, because of the perceived brand recognition. There are several ways that subsequent works can be related to the chronology of the original. Various neologisms have been coined to describe them.
Classifications.
The most common approach is for the events of the second work to directly follow the events of the first one, either resolving remaining plot threads or introducing a new conflict to drive the events of the second story. This is often called a direct sequel. 
A legacy sequel is a work which follows the continuity of the original work(s), but takes place further along the timeline, often focusing on new characters with the original ones still present in the plot. Legacy sequels are sometimes also direct sequels that ignore previous installments entirely, effectively retconning preceding events. An example of this is "Halloween" (2018) which is a direct sequel to "Halloween" (1978). When a work is set in the same universe, yet has very little if any narrative connection to its predecessor, and can stand on its own without a thorough understanding of the series, the work can be referred to as a standalone sequel. ', "2 Fast 2 Furious", ', "Shrek Forever After", ', "Son of the Mask", "Cars 3", ' and the upcoming films "Spirit Untamed", "", and "The Suicide Squad" are examples of standalone movie sequels. A sequel to the first sequel might be referred to as a "third installment", a threequel, or a second sequel.
An installment that is made following the original product but portrays events prior those of the original work is called a prequel. Parallels, paraquels, or sidequels are stories that run at the same point in time within the timeline of the story. For example, in "The Lion King 1½", Timon and Pumbaa tell their adventures that took place during the events of "The Lion King". 
Midquel is a term used to refer to works which take place between events. There are different types of "midquels", such as interquels. Interquels are stories that take place in between two preceding stories and serve as a sequel to one, and a prequel to another simultaneously. For example, if 'movie C' is an interquel of 'movies A' and 'B', the events of 'movie C' take place after the events of 'movie A', but before the events of 'movie B'. "Rogue One" of the "Star Wars" Saga is an "interquel" since it takes place between ' and '. Intraquels on the other hand are works which focus on events that place between the events of a single film. Examples include "" which takes place during Christmas between the beginning and the end of "Beauty and the Beast", and "Bambi II", which takes place during the gap between the death of Bambi's mother and the character's reappearance as a young adult in "Bambi". Other Disney films like "The Fox and the Hound 2" are additional examples of this type of sequel.
History.
In "The Afterlife of a Character", David Brewer describes a reader's desire to "see more", or to know what happens next in the narrative after it has ended.
Sequels of the novel.
The origin of the sequel as it is conceived in the 21st century developed from the novella and romance traditions in a slow process that culminated towards the end of the 17th century.
The substantial shift toward a rapidly growing print culture and the rise of the market system by the early 18th-century meant that an author's merit and livelihood became increasingly linked to the number of copies of a work he or she could sell. This shift from a text-based to an author-centered reading culture led to the "professionalization" of the author — that is, the development of a "sense of identity based on a marketable skill and on supplying to a defined public a specialized service it was demanding." In one sense, then, sequels became a means to profit further from previous work that had already obtained some measure of commercial success. As the establishment of a readership became increasingly important to the economic viability of authorship, sequels offered a means to establish a recurring economic outlet.
In addition to serving economic profit, the sequel was also used as a method to strengthen an author's claim to his literary property. With weak copyright laws and unscrupulous booksellers willing to sell whatever they could, in some cases the only way to prove ownership of a text was to produce another like it. Sequels in this sense are rather limited in scope, as the authors are focused on producing "more of the same" to defend their "literary paternity". As is true throughout history, sequels to novels provided an opportunity for authors to interact with a readership. This became especially important in the economy of the 18th century novel, in which authors often maintained readership by drawing readers back with the promise of more of what they liked from the original. With sequels, therefore, came the implicit division of readers by authors into the categories of "desirable" and "undesirable"—that is, those who interpret the text in a way unsanctioned by the author. Only after having achieved a significant reader base would an author feel free to alienate or ignore the "undesirable" readers.
This concept of "undesirable" readers extends to unofficial sequels with the 18th century novel. While in certain historical contexts unofficial sequels were actually the norm (for an example, see Arthurian literature), with the emphasis on the author function that arises in conjunction with the novel many authors began to see these kinds of unauthorized extensions as being in direct conflict with authorial authority. In the matter of "Don Quixote" (an early novel, perhaps better classified as a satirical romance), for example, Cervantes disapproved of Alonso Fernández de Avellaneda's use of his characters in "Second Volume of the Ingenious Gentleman Don Quixote of La Mancha", an unauthorized sequel. In response, Cervantes very firmly kills the protagonist at the end of the Second Part to discourage any more such creative liberties. Another example is Samuel Richardson, an 18th-century author who responded particularly strongly against the appropriation of his material by unauthorized third parties. Richardson was extremely vocal in his disapproval of the way the protagonist of his novel "Pamela" was repeatedly incorporated into unauthorized sequels featuring particularly lewd plots. The most famous of these is Henry Fielding's parody, entitled "Shamela".
In "To Renew Their Former Acquaintance: Print, Gender, and Some Eighteenth Century Sequels", Betty Schellenberg theorizes that whereas for male writers in the 18th century sequels often served as "models of paternity and property", for women writers these models were more likely to be seen as transgressive. Instead, the recurring readership created by sequels let female writers function within the model of "familiar acquaintances reunited to enjoy the mutual pleasures of conversation", and made their writing an "activity within a private, non-economic sphere". Through this created perception women writers were able to break into the economic sphere and "enhance their professional status" through authorship.
Dissociated from the motives of profit and therefore unrestrained by the need for continuity felt by male writers, Schellenberg argues that female-authored sequel fiction tended to have a much broader scope. He says that women writers showed an "innovative freedom" that male writers rejected to "protect their patrimony". For example, Sarah Fielding's "Adventures of David Simple" and its sequels "Familiar Letters between the Principal Characters in David Simple" and "David Simple, Volume the Last" are extremely innovative and cover almost the entire range of popular narrative styles of the 18th century.
Video games.
As the cost of developing a triple-A video game has risen, sequels have become increasingly common in the video game industry. Today, new installments of established brands make up much of the new releases from mainstream publishers and provide a reliable source of revenue, smoothing out market volatility. Sequels are often perceived to be safer than original titles because they can draw from the same customer base, and generally keep to the formula that made the previous game successful.
Media franchises.
In some cases, the characters or the settings of an original film or video game become so valuable that they develop into a series, lately referred to as a media franchise. Generally, a whole series of sequels is made, along with merchandising. Multiple sequels are often planned well in advance, and actors and directors may sign extended contracts to ensure their participation. This can extend into a series/ franchise's initial production's plot to provide story material to develop for sequels called sequel hooks. 
Box office.
Movie sequels do not always do as well at the box office as the original, but they tend to do better than non-sequels, according to a study in the July 2008 issue of the "Journal of Business Research". The shorter the period between releases, the better the sequel does at the box office. Sequels also show a faster drop in weekly revenues relative to non-sequels.
Sequels in other media.
Sequels are most often produced in the same medium as the previous work (e.g. a film sequel is usually a sequel to another film). Producing sequels to a work in another medium has recently become common, especially when the new medium is less costly or time-consuming to produce.
A sequel to a popular but discontinued television series may be produced in another medium, thereby bypassing whatever factors led to the series' cancellation. 
Some highly popular movies and television series have inspired the production of multiple novel sequels, sometimes rivaling or even dwarfing the volume of works in the original medium.
For example, the 1956 novel "The Hundred and One Dalmatians", its 1961 animated adaptation and that film's 1996 live-action remake each have a sequel unrelated to the other sequels: respectively "The Starlight Barking" (1967), "" (2003, direct to video) and "102 Dalmatians" (2000).
Unofficial sequels.
Sometimes sequels are produced without the consent of the creator of the original work. These may be dubbed unofficial, informal, unauthorized, or illegitimate sequels. In some cases, the work is in the public domain, and there is no legal obstacle to producing sequels. An example would be books and films serving as sequels to the book "The Wonderful Wizard of Oz," which is in the public domain (as opposed to its 1939 film adaptation). In other cases, the original creator or their heirs may assert copyrights, and challenge the creators of the sequels.
References.
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