The Communist Party of the Soviet Union (CPSU), formerly known as the Russian Communist Party (Bolsheviks) and All-Union Communist Party (Bolsheviks) and sometimes referred to as the Soviet Communist Party, was the founding and ruling political party of the Soviet Union. The CPSU was the sole governing party of the Soviet Union until 1990 when the Congress of People's Deputies modified Article 6 of the 1977 Soviet Constitution, which had previously granted the CPSU a monopoly over the political system.
The party started in 1898 as the Russian Social Democratic Labour Party. In 1903, that party split into a Menshevik (minority) and Bolshevik (majority) faction; the latter, led by Vladimir Lenin, is the direct ancestor of the CPSU and is the party that seized power in the October Revolution of 1917. Its activities were suspended on Soviet territory 74 years later, on 29 August 1991, soon after a failed coup d'état by conservative CPSU leaders against the reforming Soviet president and party general secretary Mikhail Gorbachev.
The CPSU was a communist party based on democratic centralism. This principle, conceived by Lenin, entails democratic and open discussion of policy issues within the party, followed by the requirement of total unity in upholding the agreed policies. The highest body within the CPSU was the Party Congress, which convened every five years. When the Congress was not in session, the Central Committee was the highest body. Because the Central Committee met twice a year, most day-to-day duties and responsibilities were vested in the Presidium (previously the Politburo), the Secretariat and the Orgburo (until 1952). The party leader was the head of government and held the office of either General Secretary, Premier or head of state, or two of the three offices concurrently, but never all three at the same time. The party leader was the de facto chairman of the CPSU Politburo and chief executive of the Soviet Union. The tension between the party and the state (Council of Ministers of the Soviet Union) for the shifting focus of power was never formally resolved.