King of Prussia (1861–1888) and German Emperor (1871–1888)
William I (Wilhelm Friedrich Ludwig; 22 March 1797 – 9 March 1888), or Wilhelm I, was King of Prussia from 1861 and German Emperor from 1871 until his death in 1888. A member of the House of Hohenzollern, he was the first head of state of a united Germany. He was head of state of Prussia from 1858, when he became regent for his brother Frederick William IV. During the reign of his grandson Wilhelm II, he was known as Emperor William the Great (German: Kaiser Wilhelm der Große).
https://en.wikipedia.org/wiki/William_I,_German_Emperor