John Anthony Walker Jr. was a U.S. Navy communications specialist who for almost two decades passed classified documents, including Navy code books and reports on ship/submarine movements, to agents of the Soviet Union. He later recruited a friend, his brother, and his son-- the espionage activities of the Walker spy ring has been described as among the gravest security breaches in the history of the U.S. Navy. Walker was arrested in 1985, and eventually died in prison at the age of 77.
Video on how the Walker Spy Ring's leak of information to the Russians impacted the F-14's ability to fight.
Video on Walker, his son, and the Walker Spy Ring
National Archives and Records Administration account of the Walker Spy Ring.