King Arthur, who was he?

http://www.legendofkingarthur.co.uk/battles-king-arthur.htm

 was King Arthur a real person or a folk tale? Depending on the source he might be a late Roman, a Celt; a king, a general, or a guerilla warrior fighting the Saxons, the Romans, or even the Picts in the north of England.

King Arthur may have fought a number of battles from Badon to his death perhaps at Camlann. The battles of King Arthur section details an extensive list of battles that may be attributed to him by Nennius. Nennius wrote around 800 AD, which would have been 200 years after the events that he was chronicling
The King Arthur of legend probably would have lived in post-Roman Britain. At a time when there was a power vacuum in Britain in the 5th and 6th centuries, the British had to defend themselves against several invasions. The most worrying of these invaders were the Angles and Saxons from northern Europe. It is during this fight for the control of Britain that the historical figure is thought to have lived.
Any battles King Arthur fought would probably have been against the Saxon invader, who had established themselves in the south east corner of England, and were expanding their territory both north and west. At the same time, their appear to have been Pict incursions into England from Scotland.
The soldiers of this period were not "knight in shining armour" of romance. Their main weapon was a spear and not a of a sword, and you would have been unlikely to have seen them wearing a suit of armour. Battles were generally fought to gain land, and it was not until Badon, where a British defeat of the Saxons resulted in a generation of peace.
King Arthur as a knight, in armour, on horseback, is a creation of Chretien de Troyes , written around 1170 AD and purely romantic. In other words Camelot was not presented as an historical, but as a fictional location, using as inspiration that earlier writers had written, and he certainly was not presenting his work as original "scholarship". Chretien de Troyes is the man that created Camelot, Lancelot, and the Holy Grail.
In the era of King Arthur, life for the people was in barter-based economy, based on agriculture. There was only a small amount of trade with continental Europe, but items, such as clothing, were manufactured in Britain. The typical dress of native Britons was a tunic and trousers. Houses were of wood and thatch, with a central hall that was the social centre of the community.
King Arthur almost certainly was idealised, a myth, a legend not a historical fact. The historical facts that might point to a "real" figure are few and far between, but it does not stop you admiring " the once and future king".