Sir Lancelot du Lac (meaning Lancelot of the lake, baptised as Galahad) was one of the Knights of the Round Table in the Arthurian legend. He typically features as King Arthur's greatest companion, the lord of Joyous Gard and the greatest swordsman and jouster of the age — until his adultery with Queen Guinevere is discovered, causing a civil war exploited by Mordred which brings about the end of Arthur's kingdom.
His first appearance as a main character is in Chrétien de Troyes' Le Chevalier de la Charette ("The Knight of the Cart"), written in the 12th century. Later, his exploits were expanded upon in the Prose Lancelot, which was further expanded upon for the Lancelot-Grail cycle.
Scholar Roger Sherman Loomis suggested that Lancelot is related to either the character Llenlleog the Irishman from Culhwch and Olwen (which associates him with the "headland of Gan(i)on") or the Welsh hero Llwch Llawwynnauc (probably a version of the euhemerized Irish deity Lugh Lonbemnech), possibly via a now-forgotten epithet like "Lamhcalad". Traditional scholars thought that they are the same figure due to the fact that their names are similar and that they both wield a sword and fight for a cauldron in Preiddeu Annwn and Culhwch.
Modern scholars are less certain. One suggestion has been that the name may have been an invention by Chretien de Troyes, given the manuscript evidence of L'Ancelot, since "ancelot" means "servant." Another suggestion is that the name may have been derived from Geoffrey of Monmouth's Anguselaus. However, one scholar has suggested that Lancelot may be a variant of the name "Lancelin". Lancelot or Lancelin may have instead been the hero of an independent folk-tale which had contact with and was ultimately absorbed into the Arthurian tradition.