King Arthur is a legend, and his historical prototype cannot be verified. Judging from the historical background, it should be a figure who appeared in the late Roman Empire. The original ruler of the British Isles was the Celtic people, who accepted the rule of the Roman Empire for six centuries until the decline of the Roman Empire. There are many versions of the legend about King Arthur. Due to the withdrawal of troops from Britain in the late Roman Empire, the Celts could not resist the continuous invasion of Saxons and eventually lost their sovereignty over Britain. The legendary King Arthur is a figure in the background of this era. The Celts were ruled by Rome, and King Arthur was the hero who led the Celts against the Saxons. This is a widely accepted version of the legend. Later, the Anglo-Saxons, the ruler of Britain, also transformed the legend of King Arthur and gave him the image of a hero in Britain. This version is also widely circulated. The legend that King Arthur is the son of the Roman emperor should be just one version of many legends.