Geoffrey of Monmouth, c.1100-1154, English author. He was probably born at Monmouth and was of either Breton or Welsh descent. In 1152 he was named bishop of St. Asaph in Wales. His Historia regum Britanniae (written c.1135), supposedly a chronicle of the kings of Britain, is one of the chief sources of the Arthurian legend. Geoffrey was the first to write a coherent account of Arthur, establishing the great warrior as a national hero, the conqueror of Western Europe. He drew information from the writings of Bede, Gildas, Nennius, the Welsh chronicles, and folklore, and imaginatively wove the whole into a fictional narrative in the form of a history. His work had great influence on Wace, Layamon, and many chroniclers of the Middle Ages. Another work attributed to him, the Vita Merlini (1148), also influenced later stories of Arthur and Merlin.