George F. Kennan was an American diplomat and historian, best known for his role in articulating the policy of containment during the Cold War. His influential 'Long Telegram' in 1946 outlined the strategy for countering Soviet expansion, laying the groundwork for U.S. foreign policy in the post-World War II era. Kennan's ideas were pivotal in shaping the Truman Doctrine, which aimed to provide political, military, and economic assistance to countries resisting communism.