Assuming Arthur was a real person, he probably came out of the Romanized British culture. That would make his name Artorius rather than Arthur. Find out what we know about certain Roman Britain men of the period named Artorius:
Geoffrey of Monmouth on Arthur
Timeline of Arthurian Britain / Roman Britain Timeline

Melissa Snell, About Guide to Medieval History, writes: On July 7, the new film King Arthur -- produced by Jerry Bruckheimer -- opens in theaters here in the U.S. I'm a great fan of Bruckheimer, and I fully expect this film to be exciting, well-crafted, multilayered, with at least a touch of humor -- and probably a lot of fun. What I don't expect it to be is "historically accurate."
Arthur-Mania!