Le Morte d’Arthur

"Le Morte d’Arthur" is a compilation of Arthurian romances put together by Sir Thomas Malory and contains both old English legends and original work written by Malory himself. The 1450s are considered the start of Malory’s writing of the book, with the first edition being published in 1485 by William Caxton. To this day, the compilation is considered the best-known English Arthurian legend.
Authorship.
While the exact identity of the author of "Le Morte d'Arthur" has been questioned, Thomas Malory born in 1416 in Newbold Revel, Warwickshire, England to Sir John Mallory has been most widely accepted by scholars as its author.
Malory had engaged in criminal activities including theft, attempted murder of Humphrey Stafford, 1st Duke of Buckingham, accusations of rape, and robbery. Malory was imprisoned in several prisons and managed to escape multiple times. In 1461, King Henry VI granted him a pardon. However, he was imprisoned again in 1468 because of his allegiance to the House of Lancaster and his plot to overthrow King Edward IV. He was imprisoned at Newgate Prison in London, where he most likely wrote "Le Morte d'Arthur." Henry VI returned to the throne in 1470 and Malory was thus released from prison again. He died only five months later.
The other likely candidate for the authorship of "Le Morte d'Arthur" is Thomas Mallory of Papworth St Agnes in Huntingdonshire. This theory was put forth by T. A. Martin in the Athenaeum magazine in September 1897. 
Manuscript history.
Until 1934, William Caxton’s printed edition of 1485 was thought to be the earliest surviving version of Malory’s text. However, that year Walter Oakeshott (a librarian at Winchester College) was collecting the college’s most interesting books when he discovered a manuscript. He discovered that the text had been written in years between 1471 and 1483 by two scribes working together.
Clues on its pages proved this was one of the manuscripts used by William Caxton in the preparation of his "Le Morte D'Arthur". Pages fresh from the press had been laid on the manuscript and the wet ink accidentally transferred reversed images of Caxton’s distinctive typefaces. So it is probable that the manuscript was in Caxton’s Westminster workshop during the early 1480s. The printer may even have borrowed the manuscript from one of Malory’s family members.
There is much debate over the way in which these two versions relate to each other. Field observes, however, that certain drastic and deliberate changes are made. Scholars continue to debate whether Caxton or Malory authorized these alterations. Roland argues that the differences between the Caxton and Winchester versions of this narrative suggest that Caxton "overwrote his copy text to comply with his world view, just as Malory had overwritten his source texts before him," and observes that the Roman Wars accounts in both Caxton and Malory's versions are informed by "almost four hundred years of struggles for dominion over the east and a gradual slipping away of the conquests made by the First Crusade". According to Roland, Caxton's version of the Roman War and his possible amendments to the Morte are a direct response to contemporary fears of Turkish expansion. In addition, she discovers that Malory's "Morte" was "written in the arc of an ascending fear of the Turks, an arc that reaches its zenith just as Caxton publishes Malory's work in the mid-1480s, a time when Europe was awash in uncertainty as to the repercussions of Mehmed II's death". For these reasons, the emphasis on crusades and on fears of foreign invasion begin to take on a deeper significance when the context of the Winchester and Caxton versions is considered.
Printed edition by William Caxton.
Thomas Malory’s "Le Morte D’Arthur" was first printed by William Caxton, who is generally accepted to be the first printer in England. The printing of the first edition was carried out in 1485 by Caxton’s printing house and has been of great significance, since Caxton’s printed version allowed for further distribution and printing by other printing houses. Further printing of Malory’s text by different English printers is what allowed the creation of the canonical text of Arthurian literature in the English language, as this piece of writing became more widely distributed. During the times of Victorian Britain, Malory’s first printed version, and the whole genre of English Arthuriana, gained great popularity within the academia, as well as the general population. What was especially praised was Malory’s treatment of the topic of violence, which abundantly occurs in the legend. The occurrences of killings and rape were treated with a sense of religious significance and later act as patriotic and sacred, rather than barbaric and immoral, causing the text to become a symbol of morality and Godly ideology. Furthermore, it is not only Malory’s text that was praised. William Caxton and his printed edition were greatly valued by Victorian scholars, too. It was regarded as Caxton’s most influential production. The academia generally agreed that if it was not for Caxton’s agreement to print Malory’s text, English literature might have moved in a very different direction, or been radically altered, even. Although there are several different versions of Malory’s text, each is used for different purposes, as each was published with an altered, mostly modernized, version of the language.
Language.
"Le Morte D’Arthur" was written in Middle English, a period of the English language in 11th to 15th century England. Published in 1485, the year of Thomas Malory’s writing corresponds with the end of the Medieval English era. In comparison to Geoffrey Chaucer’s "Canterbury Tales", a significant piece of writing written in typical Middle English style, Malory’s language and use of English are much closer to Early Modern English. Although Chaucer’s writing was published 85 years before Malory’s, their work belongs to the same historical and language period, and as such are often compared, especially language-wise. Although the spelling of Malory’s text does not necessarily correspond with the spelling of Early Modern English, from a grammatical and lexical point of view, it reads similarly to early Elizabethan English. The reason for the modernization of Malory’s writing is believed to be the inspiration in French texts, which gave Thomas Malory the foundation for his story. It is generally agreed that the French language was what so heavily influenced Malory’s own style of writing, as it is with high probability what modernized the language. Concerning the style specifically, Thomas Malory has been both criticized and praised for his rich usage of connecting words such as “so–and–then,” usually used to transition between stories, and for his lengthy and repetitive sentences and phrases, which some scholars condemned as too simplistic, others have, however, praised it to be of high aesthetic quality. 
Influence from other sources.
Book I.
Malory's first book's storyline is mainly based on the Prose Merlin in the "Post-Vulgate Suite du Merlin".
Book II.
This book is based mainly on the first half of the Middle English heroic poem "Alliterative Morte Arthure", which is mostly based on  "Geoffrey of Monmouth"’s p"seudo-chronicle Historia Regum Britanniae."
Book III.
This book is based on parts of the French "Prose Lancelot", mostly its "'Agravain"' section, along with the chapel perilous episode taken from "Perlesvaus".
Book IV.
Unlike most of the material in the preceding books, this specific one is not directly based on any preexisting literature. Instead, it is inspired by several Arthurian romances of the Fair Unknown genre, also known as "Le Bel Inconnu", or "Sir Gingalain" 
Book V.
That is the longest of his eight books, it is based primarily on the lengthy "Prose Tristan" in French, or the lost English translation of it, and also could be from the Middle English verse romance "Sir Tristram".
Book VI.
For this lengthy book, the main source is "The Vulgate Queste del Saint Graal", which details the exploits of numerous knights in their mythical search for the Holy Grail.
Book VII.
In this book, Malory explicitly mentions the adultery of Guinevere and Lancelot. He combined the story from both the "Vulgate Cycle prose Lancelot" (counting the story of the Fair Maiden of Astolat and an abridged retelling of "Lancelot, the Knight of the Cart") and his own creative setups.
Book VIII.
For writing his final book, he used the version of Arthur's death derived primarily from parts of the "Vulgate Mort Artu", and as a secondary source, he used the "English Stanzaic Morte Arthur."