The office of Premier of the Soviet Union was synonymous with head of government of the Union of Soviet Socialist Republics (USSR). Twelve individuals became premier over the time span of the office. Two of the twelve premiers died in office of natural causes (Vladimir Lenin and Joseph Stalin), three resigned (Alexei Kosygin, Nikolai Tikhonov and Ivan Silayev), and three held the offices of party leader and premier simultaneously (Lenin, Stalin and Nikita Khrushchev). The first premier was Lenin, who was inaugurated in 1922 after the Treaty on the Creation of the USSR. Ivan Silayev spent the shortest time in office at 126 days in 1991. At over fourteen years, Kosygin spent the longest time in office, and became the only premier to head more than two government cabinets; he died shortly after his resignation in 1980.