Wilhelm II (Friedrich Wilhelm Viktor Albert; 27 January 1859 – 4 June 1941), anglicised as William II, was the last German Emperor (German: Kaiser) and King of Prussia, reigning from 15 June 1888 until his abdication on 9 November 1918. Despite strengthening the German Empire's position as a great power by building a powerful navy, his tactless public statements and erratic foreign policy greatly antagonized the international community and are considered by many to be one of the underlying causes for World War I. When the German war effort collapsed after a series of crushing defeats on the Western Front in 1918, he was forced to abdicate, thereby marking the end of the German Empire and the House of Hohenzollern's 300-year reign in Prussia.

Wilhelm II was the son of Prince Frederick William of Prussia and Victoria, Princess Royal. His father was the son of Wilhelm I, German Emperor, and his mother was the eldest daughter of Queen Victoria of the United Kingdom and Prince Albert of Saxe-Coburg and Gotha. Wilhelm's grandfather, Wilhelm I, died in March 1888. His father became Emperor Frederick III, but died just 99 days later, and, in what is called the Year of the Three Emperors, Wilhelm II ascended the throne of the Second Reich in June 1888.

In March 1890, Wilhelm II dismissed the German Empire's powerful longtime Chancellor, Otto von Bismarck, and assumed direct control over his nation's policies, embarking on a bellicose "New Course" to cement its status as a leading world power. Over the course of his reign, the German colonial empire acquired new territories in China and the Pacific (such as Kiautschou Bay, the Northern Mariana Islands, and the Caroline Islands) and became Europe's largest manufacturer. However, Wilhelm often undermined such progress by making tactless statements and threats towards other countries without first consulting his ministers. Britain became Germany's main enemy when the Kaiser launched a massive expansion of the Imperial German Navy. By 1910 Germany had two allies left: the weak Austria-Hungary and the declining Ottoman Empire.

Wilhelm's reign culminated in Germany's guarantee of military support to Austria-Hungary during the crisis of July 1914, one of the immediate causes for World War I. By this time Wilhelm had lost virtually all decision-making power. Indeed all civilian officials were losing power to the Army's General Staff. By August 1916, a de facto military dictatorship set national policy for the rest of the conflict. Despite emerging victorious over Russia and obtaining significant territorial gains in Eastern Europe, Germany was forced to relinquish all its conquests after a decisive defeat on the Western Front in the fall of 1918. Losing the support of his country's military and many of his subjects, Wilhelm was forced to abdicate during the German Revolution of 1918–1919. The revolution converted Germany from a monarchy into an unstable democratic state known as the Weimar Republic. Wilhelm fled to exile in the Netherlands where he remained during its occupation by Nazi Germany in 1940. He died there in 1941.