Two entries with the name Oswald.
A nobleman at the court of Aurelius Ambrosius.
The Birth of Merlin, or the Childe Hath Found His Father | Attributed to William Shakespeare and William Rowley, 1662
Once Arthur’s ally against the Picts, he went to war with Arthur over Britain and over Emmeline, the daughter of the Duke of Cornwall. Arthur won the war, but Oswald and his sorcerer Osmond kidnapped Emmeline. Arthur reclaimed her in single combat against Oswald. Arthur let Oswald retain the the throne of Kent.
King Arthur; or, the British Worthy | John Dryden, 1691