Oleg Antonovich Gordievsky was a colonel of the KGB who became KGB resident-designate and bureau chief in London and a British spy.
Gordievsky in 2007
Gordievsky with U.S. President Ronald Reagan in 1987
Aldrich Hazen Ames was an American counterintelligence officer with the Central Intelligence Agency who was convicted of espionage on behalf of the Soviet Union and Russia in 1994.
Oleg Gordievsky
…the CIA had conducted a covert operation to discover who the source was. After about a year, they realised that it must be Gordievsky. A CIA officer, Aldrich Ames, began selling secrets to the KGB and reported Gordievsky's treachery to Soviet counterintelligence. Ames first met and sold classified information to…
Ames's portrait in the 1958 McLean High School yearbook
Replacement of the mailbox used by Ames; a horizontal chalk mark above the USPS logo at 37th and R Streets, Washington, D.C., was a signal that a meeting with the Soviets was needed. The original mailbox is now housed in the International Spy Museum.
FBI photo of the mailbox featuring the horizontal chalk mark placed by Ames on October 13, 1993, to arrange a meeting with his Russian intelligence handlers.