Penkovsky was a high-ranking Soviet military intelligence (GRU) officer who spied for the UK and the U.S. during the Cold War. He became the U.S.’s best human intelligence asset in the Soviet Union, providing valuable information about the Soviet placement of missiles in Cuba, including details that allowed the U.S. to identify the missile sites. After surveillance, Penkovsky was arrested by the KGB on October 22, 1962 and was later executed for treason.