According to Wikipedia: There is disagreement about whether Arthur, or a model for him, ever actually existed, or whether he is a mythic figure who has been given a historicised setting.[1]. His title of 'King' is moot: in the earliest mentions and in Welsh texts, he is never given the title 'King'. An early text refers to him as a dux bellorum ('war leader'), and medieval Welsh texts often call him ameraudur ("emperor" in the pre-Medieval sense of the Latin imperator, i.e. "commander".)... One school of thought believes that Arthur had no historical existence, that he originally was a half-forgotten Celtic deity that devolved into a personage,...
I am convinced that King Arthur was a historical figure. I have an excellent book on the matter which I find tremendously convincing and which I shall find later to share it.
I find this subject very facinating. I have a bad habit of gulping down legends at face value (a romantic - fool). Many accounts have him as a romano-british(mixed celtic-roman-welsh) leader whom repelled early saxons, or at least pushed them back and out of established communities. Authentic documentation rare at this point in history due to the onset of the dark ages. In Britian especially so. Then you add in all the romantically flavored writtings of Mallory and other Europeans in the middle-ages. Every nation adding their own favorite hero to the Authurian legend. Parsifal from Germany, Lancelot from France etc. I think there must have been some kind of very charismatic war leader 490s-550s in Britian, whos fame had over-reached his actual demesne. If I was forced to put money on it : http://en.wikipedia.org/wiki/Ambrosius_Aurelianus
He was a grandson of the Roman emperor Constantine, according to some records. He was one of the last kings before the Saxons took over, when most of the ancient Welsh records were destroyed by them.
I think he was real: I recall reading something about a Bishop in the 7th century bitching about an "Artorius" as an "Enemy of God" since he started taxing churches or something. I know Monmouth mentions him (but of course, nobody likes Monmouth, so fine, then). He was probably just some warlord somewhere. Not that uncommon a name, really.
I think this man sums it up best: John Morris - "The Age of Arthur" (1973) "The personality of Arthur is unknown and unknowable. But he was as real as Alfred the Great or William the Conqueror; his impact upon future ages mattered as much, or more so. Enough evidence survives from the hundred years after his death to show that reality was remembered for three generations, before legend engulfed his memory. More is known of his achievement, of the causes of his sovereignty and of its consequences than of the man himself. His triumph was the last victory of western Rome; his short-lived empire created the future nations of the English and the Welsh; and it ws during his reign and under his authority that the Scots first came to Scotland. His victory and his defeat turned Roman Britain into Great Britain. His name overshadows his age."
He(?) is/was both Arthur was a man, by stipulation, and yes he is a mythic character, now,:bugeye: as there is no historical evidence, other than the myth, of his being.
King Arthur and the Round Table may have been myth, but King Arthur was based on a real life Roman who was appointed as Dux Bellorum and who held off the Anglo-Saxon invasions/migrations for years. The highlight of this "Arthur" being the Battle of Mount Badon (Mons Badonicus). In total he is credited for leading the Briton/Romans in 12 battles.
The Roman Catholic Augustine did not like the Celtic Christian church (non RC), and so, destroyed their leaders and their ancient records at around 600 A.D., this was about a hundred years after King Arthur, who was a grandson of the the Roman emperor Constantine.