A twelfth-century cleric of whom little is known, writing British historiography in Latin for Norman patrons, Geoffrey of Monmouth achieved widespread and long-lasting success through introducing to a wide audience two figures from Welsh legend: Arthur and Merlin. As he hailed from a border-town, his origins could have been either Breton (Monmouth was ruled by Bretons after 1075) or Welsh. By 1129 he had moved to Oxford, where he was probably a secular canon at the College of St George, and allegedly received an “old British book” from the town's archdeacon. His death probably occurred before 1155.
Geoffrey wrote three works dedicated to a group of politically important men: Robert of Gloucester, king Stephen and Alexander …
Weiss, Judith. "Geoffrey of Monmouth". The Literary Encyclopedia. First published 24 January 2002
[https://www.litencyc.com/php/speople.php?rec=true&UID=1715, accessed 19 November 2019.]