William I, or in German Wilhelm I. (full name: William Frederick Louis of Hohenzollern, German: Wilhelm Friedrich Ludwig von Hohenzollern), 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. 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 a staunch conservative, more open to certain classical liberal ideas than his grandson Wilhelm II.
During his reign William was the commander-in-chief of the Prussian forces in the Second Schleswig War against Denmark in 1864 and the Austro-Prussian War in 1866. After the latter was won by Prussia, William wanted to march on to Vienna and annex Austria but Bismarck and Crown Prince Frederick talked him out of it. Bismarck wanted to end the war quickly, so as to allow Prussia to ally with Austria if it needed to at a later date; Frederick was also appalled by the casualties and wanted a speedy end to hostilities. During a heated discussion Bismarck threatened to resign if William continued to Vienna; Bismarck got his way.
In 1867, the North German Confederation was created, as a federation (federally organised state) of the North German and Central German states. William became the bearer of the Bundespräsidium, the federal presidium. Not expressis verbis, but in function he was the head of state. Bismarck intentionally avoided a title such as Präsident as sounding too republican. William became also the constitutional Bundesfeldherr, the commander of all federal armed forces. Via treaties with the South German states, he became commander also of their armies in case of war. In 1870, during the Franco-Prussian War, William was in command of all the German forces at the crucial Battle of Sedan.
During the Franco-Prussian War, the South German states joined the North German Confederation. The country was renamed Deutsches Reich (the German Empire), and the title of Bundespräsidium was amended with the title Deutscher Kaiser (German Emperor). This was decided on by the legislative organs, the Reichstag and Bundesrat, and William agreed to this on 18 December in the presence of a Reichstag delegation. The new constitution and the title Emperor came into effect on 1 January 1871.
William died on 9 March 1888 in Berlin after a short illness. He was buried on 16 March at the Mausoleum at Park Charlottenburg.