Which English author included the Holy Grail quest in Le Morte d'Arthur?

Thomas Malory included the Holy Grail quest in Le Morte d’Arthur, his major English compilation of Arthurian legends.

Written in the 15th century, Le Morte d’Arthur brings together stories about Arthur, Merlin, Guinevere, Lancelot, the Round Table, and the downfall of the kingdom. Its Grail quest is undertaken by a select group of knights, including Galahad, Percival, and Bors.

Malory’s treatment reflects the Christianized Grail tradition that had developed in French prose romances. Galahad is presented as the exceptionally pure knight who achieves the highest spiritual vision. Lancelot, despite his greatness as a warrior, is limited by his moral failings and cannot fully attain the same reward.

William Caxton printed the work in 1485, giving it a wide audience in English. The book strongly influenced later English-language ideas about King Arthur and the Grail, even though it is a compilation rather than a single newly invented legend.