Peter III of Russia
Following the capture of Finland from Sweden by Russia in 1809, Finland kept the Swedish constitution formally intact and became an autonomous region within the Russian Empire under the title of Grand Principality of Finland. The Russian Emperor wielded the powers formerly reserved for the King of Sweden as the Grand Prince of Finland, creatively applying the autocratic Swedish constitution of 1772 and 1789. The first Grand Prince, Alexander I of Russia, was the grandson of Duke Peter of Holstein-Gottorp, who had held the imperial throne for just 6 months in 1762 as Peter III of Russia.