Wunder
A king who owned the magical Floating Chessboard, which was sought by Gawain for Arthur.
King Wonder would only give the chessboard to Gawain if Gawain retrieved for him the magic Sword with Two Rings. This sent Gawain on a series of quests, but he eventually returned to King Wonder with the Sword with Two Rings and exchanged it for the chessboard.
Source
Roman van Walewein | Penninc and Pieter Vostaert, mid to late 13th century