General Secretary is a title most often used in political parties, and is usually the leader of the party. The General Secretary (sometimes called First Secretary or Secretary-General) is usually the leader of the Secretariat and the Politburo.
On April 3, 1922, Joseph Stalin became General Secretary of the Communist Party of the Soviet Union and had the job of deciding who was a member of the party and where they went. Vladimir Lenin was de facto leader at the time. Once Lenin died, Stalin used his power to give allies jobs in the party to become more powerful than everybody else.