Wilhelm, Duke of Saxe-Weimar (b. Altenburg, 11 April 1598 - d. Weimar, 17 May 1662), was a duke of Saxe-Weimar. Wilhelm was the fifth (and third surviving) son of Johann, Duke of Saxe-Weimar and Dorothea Maria of Anhalt. He was a key ally of Gustavus Adolphus through much of the Thirty Years' War but was shunned by Axel Oxenstierna after Gustavus' death.