“Where in literature did Merlin the sorcerer first appear? In Geoffrey of Monmouth’s The History of the Kings of Britain [Historia Regum Britanniae] (1137). This Latin prose work by the English chronicler also helped build the legend of Merlin’s protégé King Arthur.”
Excerpted from: Corey, Melinda, and George Ochoa. Literature: The New York Public Library Book of Answers. New York: Simon and Schuster, 1993.