Glywys is a legendary early 5th century Welsh king, an important character in early Welsh genealogies as the eponymous founder king of Glywysing, a southeast Welsh kingdom whose heartland lay between the Tawe and the Usk. Nevertheless Glywys is believed to have become a hermit in his later life and travelled to Cornwall where he founded the church of St Gluvias near Penryn. He is sometimes referred to as the Cornish Glywys, Glywys Cernyw. He is venerated as a saint and his feast day is the 3rd of May