"King Arthur's illegitimate son who betrayed his father and lord by raising his sword in battle against him."
In early Arthurian legend, Mordred (Medraut in Welsh) was the nephew of King Arthur of Camelot. He was the child of King Lot of Orkney and Lothian, and Queen Morgause (Anna), one of Arthur's half-sisters. He was also the brother or half-brother of Sir Gawain (who defeated the Green Knight through his bravery and honesty), Sir Agravain, Sir Gaheris and Sir Gareth. In some obscure tellings Mordred is also related to Lady Elaine, daughter of King Pelles (guardian of the Holy Grail), the wife of Sir Lancelot and mother of Sir Galahad.
Mordred became a renown knight of the Round Table, but when Arthur was away at war with Lucius Tiberius of Rome, Mordred seized the throne of Camelot and seduced Arthur's queen, Guinevere. When Arthur returned, Mordred declared war against his uncle. At the Battle of Camlann, although Mordred succeeded in mortally wounding Arthur, the king killed his treacherous nephew.
In one version of the legend, Arthur learns from his advisor, the wizard Merlin, that a child born in early May would be his undoing. To avert this prophecy, Arthur ordered all children born during that time to be executed. King Lot was killed attempting to protect his son, but Mordred managed to survive the slaughter. He is later taken in by Arthur and raised like a child of the king himself. Mordred grows up to become a knight of the Round Table and friend to Lancelot, but upon learning the truth of his father's death, Mordred turns on Arthur. Mordred sides with Lancelot against Arthur, successfully wounding Arthur and causing his removal to Avalon. However, Arthur avenges himself by killing his nephew in battle.
- In The Inferno, Mordred is mentioned very briefly as Dante and Virgil travel through Cocytus' first round, Caina, which is reserved for those who've committed treachery against members of their own family ("in whom were broken breast and shadow/at one and the same blow by Arthur's hand").
- Later versions of the legend make Arthur the father of Mordred rather than his uncle, when the king is tricked into having an incestuous affair with Morgause. Arthur has a vision of his death at Mordred's hands, yet allows his son to be trained as a knight. Guinevere is seduced by Lancelot rather than by Mordred, and her adultery causes Arthur's knights to turn on one another. Mordred seizes this chance to claim power in Camelot and uses it to finally destroy Arthur, though at the cost of his own life.