Owain Danwyn (fl. 440) was a king of Rhos in Gwynedd, northwestern Wales, in the mid-5th century. He was the son of Einion Yrth ap Cunedda and the father of Cynlas Goch, probably the Cuneglasus excoriated by Gildas. Very little is known of his life. Graham Phillips and Martin Keatman proposed a theory that he was the historical figure behind the legend of King Arthur.