George William of Brandenburg (German: Georg Wilhelm) (November 13, 1595 – December 1, 1640), was margrave and elector of Brandenburg and duke of Prussia (1619–1640). His reign was marked by ineffective governance during the Thirty Years' War. George William sought to maintain neutrality, but was forced into joining the Protestant cause by his brother-in-law, Gustavus Adolphus of Sweden. After Gustavus' death, George William stayed with Sweden another two years before he made a separate peace with Ferdinand II. From 1637 until his death, he lived in self-imposed exile in Prussia.