William I, (German: Wilhelm I.; 22 March 1797 – 9 March 1888) of the House of Hohenzollern, was King of Prussia from 2 January 1861 and the first German Emperor from 18 January 1871 to his death, the first Head of State of a united Germany.
He was de facto head of state from 1858 to 1861, serving as regent for his brother, Frederick William IV.
Under the leadership of William and his Minister President Otto von Bismarck, Prussia achieved the unification of Germany and the establishment of the German Empire.
Despite his long support of Bismarck as Minister President, William held strong reservations about some of Bismarck's more reactionary policies, including his anti-Catholicism and tough handling of subordinates.
In contrast to the domineering Bismarck, William was described as polite, gentlemanly and, while staunchly conservative, more open to certain classical liberal ideas than his grandson Wilhelm II.