Anonymous 
Sir Gawayne and the Green Knight 
an Alliterative Romance-Poem (c. 1360)

According to Wikipedia: 'Gawain … is King Arthur’s nephew and a Knight of the Round Table who appears very early in the Arthurian legend’s development. He is one of a select number of Round Table members to be referred to as the greatest knight, most notably in Sir Gawain and the Green Knight. He is almost always portrayed as the son of Arthur’s sister Morgause (or Anna) and King Lot of Orkney and Lothian, and his brothers are Agravain, Gaheris, Gareth, and Mordred. In some works he has sisters as well.’