full name Wilhelm Friedrich Ludwig (1797–1888), emperor of Germany (1871–88) and king of Prussia (1861–88), who reigned during the unification of Germany under the Prussian crown.

William was born on March 22, 1797, in Berlin, the second son of Frederick William III of Prussia and his queen Louise of Mecklenburg-Strelitz (1776–1810). He entered the Prussian army in 1807 and served in the Napoleonic Wars. In 1829 he married Augusta of Saxe-Weimar (1811–90), by whom he had two children. Upon the accession of his childless brother Frederick William IV in 1840, William became heir presumptive to the Prussian throne. In 1858, after the king was declared insane, William became regent, and three years later he succeeded to the throne. A firm believer in the divine right of kings, he declared at his coronation that he “ruled by favor of God, and of no one else.”

In 1862 William appointed the Prussian statesman Otto von Bismarck his chief minister. Subsequently they embarked upon a program of unifying the German states under Prussian leadership. Their policies involved Prussia in war with Denmark in 1864 and with Austria in 1866. In 1867, after the defeat of Austria, William became head of the newly established North German Confederation. During the Franco-Prussian War (1870–71) he took personal command at the decisive Battle of Sedan. He was proclaimed German emperor in the palace at Versailles on Jan. 18, 1871, while his troops were laying siege to the city of Paris.

During his reign William firmly supported the militarism espoused by Bismarck as well as the latter’s antidemocratic and anti-Catholic policies. Two attempts to assassinate the emperor were made in 1878; on the second occasion he was seriously wounded. On his death in Berlin on March 9, 1888, his son Frederick William succeeded him as Frederick III.