#6: George Kennan '25

American diplomat and ambassador to the Soviet Union, he was largely responsible for U.S. policy during the Cold War. Kennan framed the “containment” policy intended to check Soviet expansion in Europe and Asia. From that policy stemmed the Truman Doctrine, which marked the beginning of American intervention to prevent countries from being drawn into the Soviet sphere, and the Marshall Plan, which helped rebuild Europe after World War II.