The existence of the GRU was not publicized during the Soviet era, though it was mentioned in the 1931 memoirs of the first OGPU defector, Georges Agabekov, and described in detail in the 1939 autobiography, "I Was Stalin's Agent," by Walter Krivitsky, the most senior Red Army intelligence officer ever to defect. GRU became widely known in Russia, and outside narrow confines of the Western intelligence community, during "perestroika", due partly to the writings of "Viktor Suvorov" (Vladimir Rezun), a GRU officer who defected to Great Britain in 1978 and wrote about his experiences in the Soviet military and intelligence services. According to Suvorov, even the General Secretary of the Communist Party of the Soviet Union, the country's "de facto" leader, needed to undergo a security screening to enter GRU headquarters.