King Arthur is a mythical (some say historical) king that freed England and Wales from occupation.
Arthur Pendragon ruled in the 6th century. He was raised by Sir Ector and tutored by the great wizard Merlin. He was declared King of Britain, after pulling out a sword from a stone that no one was able to remove before. In his reign, he established the Court of Camelot. Arthur received the legendary Excalibur from the Lady of the Lake, after he had broken his own sword in battle.
Through the trickery and magic of Morgan Le Fay, Arthurs half-sister Morgause gave birth to Mordred the Evil, with Arthur being the father. After this, he married Guinevere. Upon discovering an affair between his wife and his trusted knight Lancelot, he sentenced them both to death. However, Lancelot saved Guinevere from death.
When Morgan Le Fay rallied an army with Arthur's son Mordred, Arthur was struck down in battle after mortally wounding his son.
King Arthur has appeared intermittently throughout the history of DC publications. In the Golden Age this was most notably in Wonder Woman comics. In the 1980s the character was reimagined in the futuristic world Camelot 3000. In this series King Arthur, Merlin and the Knights of the Round Table are reincarnated to battle an alien invasion led by the evil Mordred and Morgaine le Fey.