Well, to be fair, his existence is debatable. Many historians do not believe this man of romance and fable every lived, yet others are certain he did indeed, and that he accomplished all that was written down.

Arthur Pendragon, from my knowledge, did indeed fight with a sword named Excalibur, did indeed serve under Merlin, however the movie I know you are referring to over-fantasized many, many parts of the story. Likely to appeal to children.