Committee for State Security
Under the Soviet Union, the Committee for State Security (Russian: Комитет государственной безопасности; Komityet Gosudarstvennoy Bezopasnosti) was usually known, in the West, as the KGB.
The KGB, in turn, was one of a long sequence of "Organs of State Security" under the Soviet government, and could trace its origin to the Okhrana of Czarist Russia. Even though the KGB was demoted from the status of a ministry (MGB) following the death of Joseph Stalin, and the attempt to gain control by the head of State Security, Lavrenti Beria, who was executed, the KGB wielded immense power.
No Western security agency had the range of responsibilities associated with the KGB. It was a civilian foreign intelligence agency, like the U.S. Central Intelligence Agency or U.K. Secret Intelligence Service. It was responsible for domestic counterintelligence, like the U.S. Federal Bureau of Investigation or U.K. Security Service. It controlled a large paramilitary Border Guards organization, which included small warships.
It not only did signals intelligence and information assurance as do the Australian Defense Signals Directorate (DSD), Canadian Communications Security Establishment (CSE), New Zealand Government Communications Security Bureau (GCSB), and the United States National Security Agency (NSA), but operated the government communications networks.
The Main Intelligence Administration of the General Staff (Russian: "Гла́вное Разве́дывательное Управле́ние", Glavnoye Razvedovatel'noye Upravlenie (GRU) was independent from the KGB, although the KGB's Third Chief Directorage was responsible for counterintelligence inside the military. There were small but powerful security and intelligence organs in the Soviet Communist Party secretariat.
No Russian agency has quite the range of authority of the KGB; the major breakup was moving foreign intelligence into the SVR, and most other functions into the FSB. Some functions, such as the Border Guards and the briefly independent signals intelligence/information assurance agency best known as FAPSI, have been, under Vladimir Putin, incorporated into the FSB.