William I, German Emperor

William I or Wilhelm I was King of Prussia from 2 January 1861 and German emperor from 18 January 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 de facto 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 Wilhelm the Great.

The second son of Prince Frederick William and Louise of Mecklenburg-Strelitz, William was not expected to ascend to the throne. His grandfather, King Frederick William II died the year he was born, and his father was crowned Frederick William III. William fought with distinction during the War of the Sixth Coalition, and afterwards he became a prominent figure within the Prussian Army.