Sir Roger Williams (1539/1540 - 12 December 1595) was a Protestant Welsh soldier of fortune. Born in Penrhos, Monmouthshire, Williams was said by Anthony Wood to have attended Brasenose College, Oxford. He spent most of his life soldiering, mainly on the continent. He was in the Netherlands fighting on behalf of William the Silent, Prince of Orange, when the latter was assassinated, and helped capture the assassin, Balthasar Gérard. Williams was recognised as an expert on military matters by his contemporaries, and wrote A brief discourse of war (1590).