Aleksey I, also known as Aleksey Mikhailovich, was the Tsar of Russia from 1645 until his death in 1676. He was the second Romanov ruler, succeeding his father, Mikhail Romanov. Aleksey's reign is noted for significant reforms, including the modernization of the military and the expansion of Russian territory. During his rule, Aleksey I faced various challenges, including internal strife and external threats. He dealt with the Cossack uprisings and the Polish-Lithuanian Commonwealth conflicts. His reign also saw the introduction of the first Russian code of laws, known as the Ulozhenie of 1649, which aimed to strengthen the legal system.