Green Knight
The Green Knight of Bretonnia is the most celebrated of figures in Bretonnian folklore; a fey knight with ivy-wreathed armor and shield, glowing eyes and a green-bladed sword, the Green Knight is a protector of Bretonnia who invariably appears when the forces of evil are despoiling the land. When not battling beastmen or Orcs & Goblins, he often acts as a final challenger to Questing Knights; forcing them to duel him and prove their worth before they are allowed to drink from the sacred waters of the Grail and be transformed into Grail Knights.
He is based on the Green Knight, a magical warrior who appears in the Arthurian mythos. Which you'd only expect, since Bretonnia is literally the grimdark take on King Arthur and his Knights of the Round Table.