In 1857, the Prussian king Frederick William IV suffered a stroke and his brother William served as regent until 1861 when he became King William I. Although conservative, William was very pragmatic. His most significant accomplishment was the naming of Otto von Bismarck as Prussian minister president in 1862. The cooperation of Bismarck, Defense Minister Albrecht von Roon, and Field Marshal Helmut von Moltke set the stage for the military victories over Denmark, Austria, and France, that led to the unification of Germany.