At the age of 78 George Kennan, the American diplomat, consented to the writing of an authorised biography. It was perhaps not surprising that Kennan, the architect of United States' containment policy, should have chosen John Lewis Gaddis, the premier historian of US foreign policy and strategy during the Cold War. The biographer and his subject tacitly agreed that the book would not come out until Kennan had passed on. Neither of them had imagined that Kennan would go on to 101 and that the biography would appear 30 years after it was commissioned.

But it has been worth the wait. Part of the reason the book succeeds is the subject itself. Kennan was unusual among diplomats of the second half of twentieth century in the extensive records that he maintained of his official and personal life, his travels and impressions. He even kept a diary of his dreams! This is a rare treasure trove for a biographer. Gaddis makes full use of the extensive access to the papers as well as the man. There have been earlier book-length studies of Kennan, but this biography is unlikely to be surpassed. Gaddis presents not just a warts-and-all portrait of Kennan but also helps us understand why his subject's flaws were also critical to his successes.

Kennan, as is well known, played a crucial role in setting the course of US policy towards the Soviet Union in the aftermath of the Second World War. His famous 'long telegram' from Moscow and his 'Mr. X' article in Foreign Affairs dispelled the notion that Washington could expect the wartime collaboration with Moscow to continue. Gaddis rightly points out that US policy was already moving in this direction and that Kennan's contribution was to present a clear and compelling statement of the need to break with past assumptions and expectations about Soviet behaviour. There were other, particularly Western European diplomats, who had a similar assessment of the ostensibly inherent tendency towards expansionism in Russian policy. If Kennan succeeded in publicising this view, and indeed coming to be inextricably identified with it, it was partly because of his timing and partly because of his eloquence. Indeed, Kennan was a master of the classical prose style and a captivating speaker too.

No sooner had the idea of 'containment' worked its way through official channels, than Kennan began to have doubts about the manner in which his ideas were translating into policy. In particular, he was worried about the shrill public rhetoric that accompanied American policy and believed that domestic institutions in the US were subverting the pursuit of a coherent and consistent grand strategy. Kennan was never a great admirer of American democracy, and his inability to appreciate the domestic bases of external policy embittered him at every turn in his official career. Kennan's character too militated against a full innings in policy planning. He was tormented by too much self-doubt and personal anguish to be able to sustain his health and balance for long periods in office. Be that as it may, his contribution to host of other policy initiatives - the Marshall Plan and transition in Japan, for instance - were critical.

Kennan quit the foreign service in 1953 and entered academe. Although he wrote elegant books on American diplomatic history and a stream of essays for over four decades, Kennan never managed to get another chance to be at the centre of policy- making. But he longed for it. Out of office, he also emerged as a trenchant critic of American misadventures in a series of countries, ranging from Vietnam to Iraq. For a short while in the 1960s, this decidedly old-fashioned diplomat even became the toast of student radicals who deplored American imperialism. When the Soviet Union collapsed, Kennan refused to derive much satisfaction from the ostensible success of his grand strategy. But his biographer has no such qualms. Gaddis' reading of the end of the Cold War is triumphalist and he is unable to understand why Kennan did not share this view. Such occasional lapses in empathy apart, this is a superb biography - well worthy of the Pulitzer Prize that it has won.