 However, the most significant for the development of the Arthurian legend are "Lancelot, the Knight of the Cart", which introduces Lancelot and his adulterous relationship with Arthur's queen Guinevere, extending and popularising the recurring theme of Arthur as a cuckold, and "Perceval, the Story of the Grail", which introduces the Holy Grail and the Fisher King and which again sees Arthur having a much reduced role.Chrétien was thus "instrumental both in the elaboration of the Arthurian legend and in the establishment of the ideal form for the diffusion of that legend", and much of what came after him in terms of the portrayal of Arthur and his world built upon the foundations he had laid.