Alexander Vasilyevich Kolchak (, – 7 February 1920) was a polar explorer and commander in the Imperial Russian Navy, who fought in the Russo-Japanese War and the First World War. During the Russian Civil War, he established an anti-communist government in Siberia—later the Provisional All-Russian Government—and was recognised as the "Supreme Ruler and Commander-in-Chief of All Russian Land and Sea Forces" by the other leaders of the White movement from 1918 to 1920. His government was based in Omsk, in southwestern Siberia.