Who was the real King Arthur?

What do the historical documents tell us about the Knight of the Round Temple? It is just a chivalric fantasy?

The story of Arthur has been handed down to us by Medieval poets and legends - but what if he actually existed and was in fact a great king in the early years of Britain''s story. Mike Ashley visits the source material and uncovers unexpected new insights into the legend: there is clear evidence that the Arthurian legends arose from the exploits of not just one man, but at least three originating in Wales, Scotland and Brittany. The true historical Arthur really existed and is distantly related to the present royal family.