King Arthur is an important figure in the mythology of Britain. He is the central character in Arthurian legends (known as the Matter of Britain), although there is disagreement about whether Arthur, or a model for him, ever actually existed and in the earliest mentions and Welsh texts he is never given the title "king". Early texts refer to him as dux bellorum ("war leader") and High Medieval Welsh texts often call him amerauder ("emperor"). However, a recent translation of newly discovered documents may have referred to him as a king.
One school of thought believes Arthur to have lived some time in the late 5th century to early 6th century, to have been of Romano-British origin, and to have fought against the Saxons. His power base was probably in either Wales, Cornwall or the west of what would become England, but controversy over the centre of his power and the extent and kind of power he wielded continues to rage.
Some members of this school, most notably Geoffrey Ashe and Fleuriot, have argued for identifying Arthur with one Riothamus, "King of the Brettones", who was active during the reign of the Roman Emperor Anthemius. Unfortunately, Riothamus is a shadowy figure of whom we know little, and scholars are not certain whether the "Brettones" he led were Britons or Bretons.
Other members suggest that Arthur should be identified as one Lucius Artorius Castus, a historical Roman of the 2nd century, whose military exploits in Britain may have been remembered for years afterward.
Another school of thought believes that Arthur is at best a half-forgotten Celtic deity devolved into a personage (citing sometimes a supposed change of the sea-god Lir into King Lear) or a possibly fictive person like Beowulf.
Subscribers to this school of thought argue that another Roman Briton of this period, for example Ambrosius Aurelianus, led the forces battling the Saxons at the battle of Mons Badonicus.
Arthur first appears in Welsh literature. In a surviving early Welsh poem, the Gododdin, (c. 594) the poet Aneirin (c. 535-600) writes of one of his subjects that "he fed black ravens on the ramparts, although he was not Arthur" – but this poem as it currently exists is full of interpolations, and it is not possible to decide if this passage is an interpolation from a later period. Possibly of an earlier date are the following poems attributed to Taliesin: The Chair of the Sovereign – which refers to "Arthur the Blessed" – Preiddeu Annwn ("The Treasures of Heaven") which mentions "the valour of Arthur" and states "we went with Arthur in his splendid labours," and the poem "Journey to Deganwy" which contains the passage "as at the battle of Badon with Arthur, chief giver of feasts, with his tall blades red from the battle which all men remember".
Another early reference to Arthur is in the Historia Britonum, attributed to the Welsh monk Nennius, who is said to have written this compilation of early Welsh history around the year AD 830. In this work Arthur is referred to as a "leader of battles" rather than as a king. Two separate sources within this compilation list twelve battles that he fought, culminating in the battle of Mons Badonicus, where he is said to have single-handedly killed 960 men. According to the Annales Cambriae, Arthur was killed at the Battle of Camlann in 537.
Arthur also appears in the Welsh tale Culhwch and Olwen, a narrative that is usually associated with the Mabinogion. In that work, Culhwch visits his court to seek his help in winning the hand of Olwen. Arthur, who is described as his kinsman, agrees to the request, and fulfills the demands of Olwen's giant father Ysbadden, which includes his hunt for the great boar Twrch Trwth, described at length by the author.
In some of the Welsh biographies of their best-known saints (also called Vitae or the "Life" of a specific saint), Arthur makes a number of appearances: for example, in the Life of Saint Illtud, he is said to be a cousin of that churchman. Many of these appearances portray Arthur as a fierce warrior, and not necessarily as morally impeccable as in later Romances. According to the Life of Saint Gildas, written in the 11th-century by Caradoc of Llancarfan, Arthur killed Gildas' brother Hueil, a pirate on the Isle of Man.
Lifris writes in his Life of Saint Cadoc that Arthur was bettered by Cadoc: Cadoc gave protection to a man who killed three of Arthur's soldiers; Arthur was awarded a herd of cattle from Cadoc as wergeld for his men; Cadoc delivered them as demanded; but when Arthur took possession of the animals, they were transformed into bundles of ferns. The likely original purpose of this story would be to promote popular acceptance of the new Christian faith by "demonstrating" that Cadoc, the Christian leader, had magical powers traditionally ascribed to Druids and of sufficient intensity to outsmart the temporal ruler, Arthur. Similar incidents are described in the late medieval biographies of Carannog, Padern, and Goeznovius.
This may be related to legends where Arthur is depicted as the leader of the Wild Hunt, a folk motif that is also recorded in Brittany, France, and Germany.