A number of individuals have put forward Cerdic as the prototype of Arthur. Perhaps the first time I ran across this hypothesis was with 'Arthur, Cerdic, and the Formation of Wessex' by John C. Rudmin and Joseph W. Rudmin (first submitted for publication in Oct 1993). Their general thesis is that by linking the sixth century Welsh king, Caradoc Vreichvras, to Cerdic of Wessex, the origin of the Arthurian legend can be explained.
   Dan Hunt pointed out that he considered it highly suspicious that Nennius' section on Arthur seems to perfectly correspond with a section of the Anglo-Saxon Chronicle. Nennius' account of Arthur begins right after we are told that Octha has become the Kentish king following the death of his father, Hengist, and ends just prior to the passage on the succession of Ida. In the Anglo-Saxon Chronicle (Parker manuscript), the entry which has Aesc succeed Hengist comes only one entry (a battle featuring Aelle and Cissa intervening) before the first appearance of Cerdic of Wessex and his son Cynric. The ASC entry which corresponds to Nennius' mention of Ida immediately follows the battles of Cerdic and Cynric.