Galahad is a Grail Knight.

Galahad was the son of Lancelot and Elaine

"The Queste is part of the compilation called the Prose Lancelot (1215-1230), which deals with the adventures of Lancelot and his love affair with Guinevere. There are warnings in the Lancelot that his adultery with Guinevere will debar him from achieving the Grail, and the author of the Queste invented a new character as the Grail-winner, Galahad, who was 'so grounded in the love of Christ that no adventure could tempt him into sin." - Richard Cavendish, "Grail", Man, Myth & Magic, An Illustrated Encyclopedia of the Supernatural, Vol. 9

"Like Perceval in Perlesvaus, Galaad after achieving the adventures of the Grail in the mainland castle sails out to sea to become the king of an island, whither the grail is transferred. There in the island city of Sarras, Galaad is first imprisoned then crowned." from Loomis, 'Celtic Myth and Arthurian Romance'.

Gawain = Galahad (island- Sarras) = Gwair (island- Lundy)

Derivation of Galahad

"A brief passage in the French text  La Queste del Saint Graal (Translated by Sir Thomas Malory)), which Malory omitted, makes the messianic role of Galahad quite clear. The venerable man in white who brought the youth to Camelot, addressing Arthur, said: 'I bring thee the desired knight (le chevalier desirÚ), who is descended from the high lineage of king David,'" "Indeed the very name Galahad was chosen to carry out this concept. Its biblical origin has long been known, since it occurs in the Vulgate Old Testament, the standard text of the Middle Ages, in the form Galaad. sometimes it refers to a place, sometimes to a person. It remained for Pauphilet [+tudes] to discover its astonishing fitness for the messianic hero of the Queste. He showed that, according to Genesis 31:47-52, Galaad meant 'heap of testimony', and that Isidore of Seville, Walafrid, Strabo, and the Venerable Bede construed this etymology as a reference to Christ." - Roger Sherman Loomis, The Grail, From Celtic Myth to Christian Symbol