Claudine, Claudino, Claudyne
According to Malory he was King Claudas’ son; according to Vulgate, he was the king’s stepson.
Claudas made Claudin co-commander-in-chief (with Chanart) of his army for the war with Arthur. Gawaine admired Claudin’s prowess in battle; Bors and Gawaine agreed that, after Lancelot and Gawaine himself, Claudin was the best knight. With Chanart and another good Gaulish knight, Esclamor (probably distinct from King Esclamor), Claudin personally welcomed Arthur into Gannes after Claudas escaped.
An excellent and noble knight, he was spared his father’s wicked disposition, and he recognized Claudas’s injustice towards Lancelot’s family.
When he learned of the Grail Quest in Britain, he traveled there and was eventually made a Knight of the Round Table. He guarded a bridge at the castle Beauregard, but was defeated by Galahad.
Claudin was one of three Gaulish knights who arrived at Carbonek to meet Galahad, Percivale, Bors, three Irish knights, and three Danish knights at the climax of the Grail Quest. Together, these twelve knights represented the twelve apostles at the Last Supper. At Carbonek they witnessed the mysteries of the Grail as performed by Joseph of Arimathea (or perhaps by his son Josephe).
From the Vulgate we learn that all but one of the knights were to die on the Quest. After leaving Carbonek, the twelve knights went on their separate ways, apparently in small groups, as the Apostles were sent forth in all directions. Since Sir Bors was the survivor, Claudin presumably died before reaching home.
Claudin would seem to be the French equivalent to Galahad, or at least to Percivale.
Sources
Vulgate Lancelot | 1215-1230
Vulgate Queste del Saint Graal | 1215-1230
Post-Vulgate Queste del Saint Graal | 1230-1240
Prose Tristan | 1230-1240