The KGB was the main security agency for the Soviet Union from 13 March 1954 until 3 December 1991. Listen to a free audiobook on the KGB: https://www.amazon.com/gp/search?ie=U…
As a direct successor of preceding agencies such as the Cheka, GPU, OGPU, NKGB, NKVD and MGB, it was attached to the Council of Ministers. It was the chief government agency of “union-republican jurisdiction”, carrying out internal security, intelligence and secret police functions. Similar agencies operated in each of the republics of the Soviet Union aside from the Russian SFSR, with many associated ministries, state committees and state commissions.
The agency was a military service governed by army laws and regulations, in the same fashion as the Soviet Army or the MVD Internal Troops. While most of the KGB archives remain classified, two online documentary sources are available. Its main functions were foreign intelligence, counter-intelligence, operative-investigative activities, guarding the state border of the USSR, guarding the leadership of the Central Committee of the Communist Party and the Soviet Government, organization and security of government communications as well as combating nationalist, dissident, religious and anti-Soviet activities.
On 3 December 1991, the KGB was officially dissolved. It was later succeeded in Russia by the Foreign Intelligence Service (SVR) and what would later become the Federal Security Service (FSB). Following the 1991–1992 South Ossetia War, the self-proclaimed Republic of South Ossetia established its own KGB, keeping the unreformed name. In addition, Belarus established its own national security agency in 1991, the State Security Committee of the Republic of Belarus, keeping the unreformed name.
The GRU (military intelligence) recruited the ideological agent Julian Wadleigh, who became a State Department diplomat in 1936. The NKVD’s first US operation was establishing the legal residency of Boris Bazarov and the illegal residency of Iskhak Akhmerov in 1934. Throughout, the Communist Party USA (CPUSA) and its General Secretary Earl Browder, helped NKVD recruit Americans, working in government, business, and industry.
Other important, low-level and high-level ideological agents were the diplomats Laurence Duggan and Michael Whitney Straight in the State Department, the statistician Harry Dexter White in the Treasury Department, the economist Lauchlin Currie (an FDR advisor), and the “Silvermaster Group”, headed by statistician Greg Silvermaster, in the Farm Security Administration and the Board of Economic Warfare. Moreover, when Whittaker Chambers, formerly Alger Hiss’s courier, approached the Roosevelt Government—to identify the Soviet spies Duggan, White, and others—he was ignored. Hence, during the Second World War (1939–45)—at the Tehran (1943), Yalta (1945), and Potsdam (1945) conferences—Big Three Ally Joseph Stalin of the USSR, was better informed about the war affairs of his US and UK allies than they were about his.
Soviet espionage was at its most successful in collecting scientific and technological intelligence about advances in jet propulsion, radar and encryption, which impressed Moscow, but stealing atomic secrets was the capstone of NKVD espionage against Anglo–American science and technology. To wit, British Manhattan Project team physicist Klaus Fuchs (GRU 1941) was the main agent of the Rosenberg spy ring. In 1944, the New York City residency infiltrated top secret Los Alamos National Laboratory in New Mexico by recruiting Theodore Hall, a 19-year-old Harvard physicist.
The KGB failed to rebuild most of its US illegal resident networks. The aftermath of the Second Red Scare (1947–57) and the crisis in the CPUSA hampered recruitment. The last major illegal resident, Rudolf Abel (Vilyam Genrikhovich Fisher/”Willie” Vilyam Fishers), was betrayed by his assistant, Reino Häyhänen, in 1957. Recruitment then emphasised mercenary agents, an approach especially successful in scientific and technical espionage, since private industry practised lax internal security, unlike the US Government. One notable KGB success occurred in 1967, with the walk-in recruitment of US Navy Chief Warrant Officer John Anthony Walker. Over eighteen years, Walker enabled Soviet Intelligence to decipher some one million US Navy messages, and track the US Navy.
In the late Cold War, the KGB was successful with intelligence coups in the cases of the mercenary walk-in recruits FBI counterspy Robert Hanssen (1979–2001) and CIA Soviet Division officer Aldrich Ames (1985–1994). https://en.wikipedia.org/wiki/KGB