Nicholas I and II were both Tsars of Russia. Nicholas I was Tsar from 1825 to 1855, while Nicholas II was Tsar from 1894 to 1917. Both Tsars were members of the Romanov dynasty, which had ruled Russia since 1613. Nicholas I was known for his authoritarian rule and for his efforts to modernize Russia, while Nicholas II is remembered for his abdication of the throne in 1917, which led to the end of the Romanov dynasty.