A man of impressive mental powers, of extraordinary intellectual range, and—last but not least—of exceptional integrity, George Frost Kennan (1904-2005) was an adviser to presidents and secretaries of state, with a decisive role in the history of this country (and of the entire world) for a few crucial years in the 1940s, after which he was made to retire; but then he became a scholar who wrote seventeen books, scores of essays and articles, and a Pulitzer Prize–winning memoir. He also wrote remarkable public lectures and many thousands of incisive letters, laying down his pen only in the hundredth year of his life.Having risen within the American Foreign Service and been posted to various European capitals, and twice to Moscow, Kennan was called back to Washington in 1946, where he helped to inspire the Truman Doctrine and draft the Marshall Plan. Among other things, he wrote the “X” or “Containment” article for which he became, and still is, world famous (an article which he regarded as not very important and liable to misreading). John Lukacs describes the development and the essence of Kennan’s thinking; the—perhaps unavoidable—misinterpretations of his advocacies; his self-imposed task as a leading realist critic during the Cold War; and the importance of his work as a historian during the second half of his long life.