The Communist Party of the Soviet Union, also shortened to CPSU, was the ruling party in Russia from 1917 until 1991. As the name suggests, tt was a totalitarian communist party, the first of it's kind in fact.
The CPSU formed out of the Bolshevik faction of the Russian Social Democratic Labour Party in 1912. As the Soviet Union wasn't officially created until 1922, the name of the party was until then the Bolshevik Russian Social Democratic Labour Party, or something to that effect. It became the Communist Party of the Soviet Union when the Soviet Union was formed in 1922, an act ratified by the 1924 Constitution.
Lenin was the original Communist leader. His position until 1924 was "Chairman of the Council of People's Commisars". Lenin was succeeded by Alexei Rykov, although Rykov was not the leader of the party. Stalin was made General Secretary in 1922, and throughout his rise to power in the 1920s, the title became synonymous with supreme leadership of the Communist Party and the Soviet Union.
Vladimir Lenin (1917 - 1924)
Josef Stalin (1922 - 1953)
Nikita Khrushchev (1953 - 1964)
Leonid Brehznev (1964 - 1982)
Yuri Andropov (1982 - 1984)
Konstantin Chernenko (1984 - 1985)
Mikhail Gorbachev (1985 - 1991)
Vladimir Ivashko (24 - 29 August 1991)