Germanys ruler during World War I?

Kaiser Wilhelm II. Interestingly enough, he was a very close relative of the British royal family, who thought it politically advisable to change their name from Saxe-Coburg and Gotha to Windsor in 1917. In fact they were cousins.

Kaiser Wilhelm II, last Kaiser of Germany, was the Commander in Chief of the German armed forces throughout the war, but his Chief of the Imperial German General Staff, Erich Georg Anton Sebastian von Falkenhayn and his successor, Paul von Beneckendorff und von Hindenburg, operated semi-independently.