Alexander Vasilyevich Kolchak was a Russian admiral, military leader and polar explorer who held the title of Supreme Ruler of Russia from 1918 to 1920 during the Russian Civil War, though his actual control over Russian territory was limited. Previously, he served in the Imperial Russian Navy and fought in the Russo-Japanese War and World War I.

The Supreme Ruler of Russia, also referred to as the Supreme Leader of Russia, was the head of state and supreme commander-in-chief of the Russian State, an anti-Bolshevik government established by the White Movement during the Russian Civil War. For nearly two years from November 1918 until April 1920, the armies of the White Movement were nominally united under the administration of the Russian State, during which the Russian State claimed to be the sole legal government of Russia. The office's sole holder for most of its existence, and the only one to officially adopt the titles and functions of the Supreme Ruler, was Admiral Alexander Kolchak, who was elected to the position by the All-Russian Council of Ministers following the November 18 coup which overthrew the Directory.