Geoffrey of Monmouth (, ) (c. 1100 – c. 1155) was a Welsh cleric and one of the major figures in the development of British historiography and the popularity of tales of King Arthur. He is best known for his chronicle ("History of the Kings of Britain"), which was widely popular in its day and was credited, uncritically, well into the 16th century, being translated into various other languages from its original Latin, but which is now considered historically unreliable.