Matter of Britain
"King" Mark of Cornwall is a semi-historical figure known from Welsh literature, from the Matter of Britain, and, in particular, from the later Norman-Breton medieval romance of Tristan and Yseult, where he appears as a close relative of King Arthur, himself usually considered to be born of the Cornish people in folklore traditions derived from Geoffrey of Monmouth's 12th-century "Historia Regum Britanniae".