Oleg Penkovsky, Russian colonel (d. 1963)
Oleg Vladimirovich Penkovsky (Russian: Олег Владимирович Пеньковский; 23 April 1919 – 16 May 1963), codenamed HERO, was a Soviet military intelligence (GRU) colonel during the late 1950s and early 1960s. Penkovsky informed the United States and the United Kingdom about Soviet military secrets, most importantly, the appearance and footprint of Soviet intermediate-range ballistic missile (IRBM) installations and the weakness of the Soviet intercontinental ballistic missile (ICBM) program. This information was decisive in allowing the U.S. to recognize that the Soviets were placing IRBMs in Cuba before most of the missiles were operational. It also gave U.S. President John F. Kennedy, during the Cuban Missile Crisis that followed, valuable information about Soviet weakness that allowed him to face down Soviet leader Nikita Khrushchev and resolve the crisis without a nuclear war.

Penkovsky was the highest-ranking Soviet official to provide intelligence for the West up until that time, and is one of several individuals credited with altering the course of the Cold War. He was arrested by the Soviets in October 1962, then tried and executed the following year.