Roger Williams (~1537 - 1595) was a Welsh soldier of fortune.

Williams was in the Netherlands fighting on behalf of William the Silent, Prince of Orange, when the latter was assassinated, and helped capture the assassin, Balthazar Gerards. Knighted after the Battle of Zutphen in 1586 by Robert Dudley, Earl of Leicester, he accompanied Sir Francis Drake to Portugal, and later fought on behalf of the French Huguenots.

Wililams is supposed to be the model for the character of Fluellen in Shakespeare's Henry V. He was recognised as an expert on military matters by his contemporaries, and wrote A brief discourse of war (1590).