Formed in 1953, the KGB was responsible for external espionage, internal counter-intelligence, and internal ‘crimes against the state’. The most famous chairman of the KGB was Yuri Andropov (1967–82) who was Soviet leader (1982–84). He made KGB operations more sophisticated, especially against internal dissidents. In 1991 the KGB was dissolved, to be replaced by five separate bodies. These pledged themselves to work with Western Intelligence in the prevention of nuclear proliferation and the development of chemical and biological weapons, and to fight terrorism and drug trafficking.