Frederick William I

Frederick William I (Friedrich Wilhelm I) may refer to:


 * Frederick William I, Duke of Saxe-Weimar (1562–1602)
 * Frederick William, Elector of Brandenburg, the "Great Elector" of Brandenburg-Prussia (1620–1688)
 * Frederick William I, Duke of Schleswig-Holstein-Sonderburg-Beck (1682–1719)
 * Frederick William I of Prussia (1688–1740)
 * Frederick William, Elector of Hesse (1802–1875)