George Frost Kennan (February 16, 1904 – March 17, 2005) was an American adviser, diplomat, political scientist, and historian, best known as "the father of containment" and as a key figure in the emergence of the Cold War. He later wrote standard histories of the relations between Soviet Union and the Western powers. He was also a core member of the group of foreign policy elders known as "The Wise Men".
In the late 1940s, his writings inspired the Truman Doctrine and the U.S. foreign policy of "containing" the Soviet Union, thrusting him into a lifelong role as a leading authority on the Cold War. His "Long Telegram" from Moscow in 1946 and the subsequent 1947 article "The Sources of Soviet Conduct" argued that the Soviet regime was inherently expansionist and that its influence had to be "contained" in areas of vital strategic importance to the United States. These texts quickly emerged as foundation texts of the Cold War, expressing the Truman administration's new anti-Soviet Union policy. Kennan also played a leading role in the development of definitive Cold War programs and institutions, notably the Marshall Plan.