(Arthurian legend) one of the knights of the Round Table; friend of King Arthur until (according to some versions of the legend) he became the lover of Arthur's wife Guinevere

In the Arthurian legend, Sir Lancelot (Lancelot du Lac, or Lancelot of the Lake; also Launcelot) is one of the Knights of the Round Table. In most of the French prose romances and works, he is characterized as the greatest and most trusted of Arthur's knights, and plays a part in many of Arthur's victories – but Arthur's eventual downfall is also brought about in part by Lancelot, whose affair with Arthur's wife Guinevere destroys the unity of Arthur's court.