From The New Arthurian Encyclopedia, edited by Norris J Lacy:
[Gustave] Doré’s most significant contribution to Arthurian art was his illustration of Tennyson’s Idylls of the King. Already famous for his editions of Dante, the Bible, Cervantes, and others, Doré was commissioned by Moxon & Co., Tennyson’s publisher, to provide thirty-six wash drawings for the immensely popular 1859 Idylls, nine for each of Tennyson’s four poems: “Enid,” “Vivien,” “Elaine,” and “Guinevere.” His work was then copied by English steel-engravers rather than being carved into wood blocks, Doré’s usual practice. The illustrated poems were issued separately in folio editions from 1867 to 1868 by Moxon in London and by Hachette in Paris (trans. Fransique Michel). In 1868, the separate editions were gathered into one volume, for which Doré added a frontispiece depicting Tennyson surrounded by his Arthurian characters, with some creatures of Doré’s invention. The illustrations were popular, especially in England, and went through several editions.