Geoffrey of Monmouth was likely born in Wales or was of Welsh ancestry. His name appears on documents that place him in Oxford between 1129 and 1151, when he was ordained into the priesthood. Though he does not directly function as a character in his narrative, he makes his presence felt as its author through direct address—both to his audience of readers and to the subjects about whom he is writing. He also foregrounds himself as translator and gatherer of information by referring to the patrons who requested he undertake the work, and his sources (the latter however specifically or vaguely).

Geoffrey claims to be translating “a certain ancient book” (37). If this book existed, there are no surviving copies of it. One theory is that the reference to the book is symbolic of Walter, Archdeacon of Oxford, recounting oral stories. As several versions of The History of the Kings of Britain exist, another theory suggests the existence of a prior author, a pseudo-Geoffrey who composed the text but allowed Geoffrey to take the credit.