A Saxon magician of treacherous character in Dryden’s King Arthur.
He was in the service of King Oswald the Saxon, Arthur’s enemy. He commanded a demon named Grimbald and an army of fiends. When Oswald kidnapped Emmeline, Arthur’s fiancée, Osmond tried to seduce her but failed. When Arthur rescued Emmeline, he threw Osmond into a dungeon.
Source
King Arthur; or, the British Worthy | John Dryden, 1691