Geoffrey was translated into a number of different Welsh prose versions by the end of the 13th century, collectively known as "Brut y Brenhinedd". One variant of the "Brut y Brenhinedd", the so-called "Brut Tysilio", was proposed in 1917 by the archaeologist William Flinders Petrie to be the ancient British book that Geoffrey translated, although the "Brut" itself claims to have been translated from Latin by Walter of Oxford, based on his own earlier translation from Welsh to Latin. Geoffrey's work is greatly important because it brought the Welsh culture into British society and made it acceptable. It is also the first record we have of the great figure King Lear, and the beginning of the mythical King Arthur figure.