During the 1970s, the US and Soviet Union were engaged in the Cold War.
The US, along with other Western countries, was a member of Nato, while the Soviet Union joined forces with central and eastern European countries in the Warsaw Pact.
After becoming frustrated with the way the Soviets controlled his country, Ryszard Kukliński, a Polish colonel, wrote to the US Embassy in Bonn, West Germany.
For the next 10 years, he would feed the CIA tens of thousands of pages of classified military secrets.
Aris Pappas, a CIA agent who analysed Ryszard's intel, speaks to George Crafer about his memories of this forgotten hero.
(Photo: Jack Strong aka Ryszard Kukliński. Credit: AP)
