Geoffrey of Monmouth (c. 1100–1154) was a scholar and probably also a monk, educated in Monmouth and living in Oxford. He was in later life Bishop of St Asaph. He wrote the work Historia Regum Britanniae (c. 1140) in Latin, which tells the ‘history’ of Britain from its founding by the Trojan Brutus up to the death of King Arthur and the return of the Saxons. Geoffrey claimed to have translated it from a ‘very old book in the British tongue’, but really he seems to have collected various chronicle, biblical, classical and folk stories – and possibly even included some of his own invention too – in order to create a British history. The work establishes the Arthurian legend and numerous other myths of British history. In the first half of the 16th century, some scholars started to express scepticism about Geoffrey’s reliability as a historian, but Historia Regum Britanniae nevertheless remained an important and influential work.
In Shakespeare’s day, the work was widely available in Latin manuscript. It had also been translated into Norman French. This manuscript, Cotton MS Nero D VIII, was created in England in the last quarter of the 12th century, with a possible Colchester provenance. It is written in Latin, with its large capitals in red and green ink with scrolled/leafy decoration. In the late-16th or early-17th century, the manuscript was owned by the historian and antiquarian John Stow.
The Historia contains the earliest known version of the story of King Leir and was a source for many later retellings, such as Holinshed and The True Chronicle History of King Leir. As such it could either have been a direct or an indirect source for Shakespeare’s King Lear.