In 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 dependent on them 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.
Lancelot is a popular character, and has been the subject of many poems, stories, plays, and films as a famous figure in the Arthurian cycle of romances. To the great majority of English readers the name of no knight of King Arthur's court is so familiar as is that of Sir Lancelot. The mention of Arthur and the Round Table at once brings him to mind to moderns as the most valiant member of that brotherhood and the secret lover of the Queen. Lancelot, however, is not an original member of the cycle, and the development of his story is still a source of considerable disagreement between scholars.
It is interesting to note that Lancelot does not appear in the earliest existing versions of the Arthurian legends. (See Geoffrey of Monmouth for an example of one who doesn't mention Lancelot, and Chretien de Troyes for one who does.) The name Lancelot is not obviously Celtic, though attempts have been made to find a possible Celtic origin that might have been corrupted into Lancelot (such as "Lance ap Lot," meaning Lance, son of Lot).