Octa may appear in Welsh Arthurian literature as Osla Bigknife, though this character may be better identified with Offa of Mercia. This Osla figures in two medieval prose tales, "Culhwch and Olwen" (c. 1100) and "The Dream of Rhonabwy" (12th- or 13th-century). In "Culhwch" he is a member of King Arthur's retinue; he is named in a list of Arthur's followers, and his weapon "Bronllavyn Short Broad", which is wide enough for Arthur's army to use as a bridge, is described. Osla later participates in the hunt for the great boar Twrch Trwyth, during which he nearly drowns when the sheath of his great knife fills with water. In "Rhonabwy" Osla is Arthur's opponent at the Battle of Badon.