After the founding of the subsequent Union of Soviet Socialist Republics (USSR or Soviet Union) in 1922, Lenin had introduced a mixed economy, commonly referred to as the New Economic Policy, which allowed for capitalist practices to resume under the Communist Party dictation in order to develop the necessary conditions for socialism to become a practical pursuit in the economically undeveloped country. In 1929, as Marshal Joseph Stalin (1878-1953, in power 1929-1953), became the leader of the party, Marxism-Leninism, a fusion of the original ideas of German Empire philosopher and economic theorist Karl Marx (1818-1883), and Lenin, became formalized as the partys guiding ideology and would remain so throughout the rest of its existence. The party pursued state socialism, under which all industries were nationalized and a planned economy was implemented. After recovering from the Second World War (1939-1945), De-Stalinization which 1965 Soviet economic reform and Khrushchev thaw under Nikita Khrushchev (1894-1971, in power 1953/1958-1964). By 1980, various factors, including the continuing Cold War (1946-1991), and ongoing nuclear arms race with the United States and other Western Europe powers and unaddressed inefficiencies in the economy, led to Era of Stagnation under Alexei Kosygin (1904-1980, in power 1964), and further with  Leonid Brezhnev (1906-1982, in power 1964-1982) and a growing disillusionment. After a younger  vigorous  Mikhail Gorbachev (b.1931), assumed leadership in 1985, (following two short-term elderly leaders who quickly died in succession), rapid steps were taken to transform the tottering Soviet economic system in the direction of a market economy once again. Gorbachev and his allies envisioned the introduction of an economy similar to Lenins earlier New Economic Policy through a program of "perestroika", or restructuring, but their reforms along with the institution of free multiparty elections led to a decline in the partys power, and after the Dissolution of the Soviet Union (1990-1991), the banning of the party by later last RSFSR President Boris Yeltsin (1931-2007, in power 1991-1999) and subsequent first President of an evolving democratic and free market economy of the successor Russian Federation.. Which leader served for the second longest number of years?