King Arthur (Welsh : Brenin Arthur, Cornish : Arthur Gernow, Breton : Roue Arzhur, French : Roi Arthur) is a legendary king of Britain, a hero of English mythology, 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.