In 1978, the FBI finally realized that Aleksei Kulak (FEDORA) was a KGB triple-agent who had duped the Bureau from the time he "volunteered" to spy for it in NYC in 1962 until he returned to Moscow in 1976. (He is believed to have died of natural causes in 1983.)
Kulak not only convinced gullible J. Edgar Hoover that
Yuri Nosenko was a true defector, but he also sent the Bureau off on a debilitating wild goose chase looking for a fictional mole whose first name was "Dick," and, by pretending to have to answer KGB's questions about American intelligence to advance his career, got the FBI to do KGB's research on the Bureau and the CIA.
(Students of the JFK assassination will remember that
Nosenko claimed the KGB didn't interview Marine Corps radar operator Lee Harvey Oswald during the two and one-half years he lived in the USSR.)
-- MWT