According to legends, King Arthur (Welsh: Brenin Arthur; Cornish: Arthur Gernow; Breton: Roue Arzhur; French: Roi Arthur) was a king of Britain. He is a folk hero and a central figure in the medieval literary tradition known as the Matter of Britain. In Welsh sources, Arthur is portrayed as a leader of the post-Roman Britons in battles against the Anglo-Saxons in the late 5th and early 6th centuries.
https://en.wikipedia.org/wiki/King_Arthur