Osla Gyllellfawr (Osla Big-Knife). A legendary Saxon leader mentioned in the medieval Welsh tales "Dream of Rhonabwy" and "Culhuwch and Olwen".
According to the "Dream of Rhonabwy", Osla (or Ossa) was Arthur's opponent at Badon.
According to the "Culhuwch and Olwen", he was one of the warriors of Arthur's Court. It is said that he carried a knife called Bronllafn Uerllydan (‘Short-broad’) so big it could act as a "bridge sufficient for the hosts of the Island of Britain". Later in the story Osla took part in the hunting of the boar Trwyth and was apparently drowned when the sheath of his knife filled with water and dragged him into the depths of the Severn.