Mikhail Sergeyevich Gorbachev was a Soviet and Russian politician who served as the eighth and final leader of the Soviet Union from 1985 to the country's dissolution in 1991. He served as General Secretary of the Communist Party of the Soviet Union from 1985 and additionally as head of state beginning in 1988, as Chairman of the Presidium of the Supreme Soviet from 1988 to 1989, Chairman of the Supreme Soviet from 1989 to 1990 and the only President of the Soviet Union from 1990 to 1991. Ideologically, Gorbachev initially adhered to Marxism–Leninism but moved towards social democracy by the early 1990s.