Emperor Nicholas I of Russia reigned from 1825 to 1855. He was the younger brother of Alexander I and ascended to the throne after his brother's death. Nicholas I is known for his autocratic rule and efforts to strengthen the central authority of the monarchy. He implemented strict censorship and maintained a powerful secret police to suppress dissent. During his reign, Nicholas I faced several challenges, including the Crimean War (1853-1856), which exposed weaknesses in the Russian military and administration. His policies aimed at modernization and military reform were initiated but largely ineffective. Nicholas I's reign ended with his death in 1855, leaving a complex legacy.