Emperor Nicholas I was the ruler of the Russian Empire from 1825 until his death in 1855. He ascended to the throne after the death of his brother, Emperor Alexander I. Nicholas I is known for his autocratic rule and efforts to modernize Russia, including military reforms and the establishment of a more centralized government. During his reign, Nicholas I faced several challenges, including the Decembrist Revolt of 1825, which was an uprising by army officers advocating for constitutional reforms. He also expanded Russian territory through military campaigns, notably in the Crimean War, which ultimately led to significant losses for Russia and affected his legacy.