It is hard to think of a more daunting biographical subject than J. Robert Oppenheimer. He understood abstruse mathematics and physics most of us cannot truly grasp, and assimilated with ease other subjects that ordinary folk never get around to - learning Sanskrit to read the Bhagavadgita being the most famous example. Even among the theoretical physics elite, his powers of apprehension were astonishing. They existed in spite of, or perhaps because of, a complex psyche. Associates found him either ineffably charming or astoundingly rude, or both. He had a pained self-consciousness second only to Hamlet. Give such a man a central role in key moments of the 20th century, most notably the Manhattan Project to build the atomic bomb, and the task of weighing the life, the work and its significance is pretty substantial.

It is also, it seems, irresistible. The reasons were vividly apparent in Oppenheimer: The Father of the Atomic Bomb, a seven-part drama series Peter Goodchild made for the BBC in 1980, an effort that also produced one of the first biographies. The protagonist¡¯s unsettled soul, along with tortured relationships, moral agonising, murky politics, double dealing and dodgy dossiers, were all indispensable parts of a story of a remarkable rise - leading the largest science and engineering project in history - and (partial) fall, with withdrawal of his government security clearance following a humiliating hearing in 1954. Add world-shattering discoveries and intimate involvements with the most brilliant minds of the era, and few figures are more fascinating.

Authors squaring up to Oppenheimer have not been hard to find since Goodchild¡¯s effort. At least six volumes about the man appeared around the time of the centenary of his birth in 2004. None, arguably, is definitive. Ray Monk, whose work follows in their wake, certainly argues that. In particular, he points out that the Pulitzer prize-winning 2005 biography American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer by Kai Bird and Martin Sherwin, while a ¡°monumental piece of scholarship¡±, is light on the physics that its subject cared about so deeply.

Monk, as in his landmark biographies of Ludwig Wittgenstein and Bertrand Russell, is interested in the whole person, and presents the physics as well as is possible in a non-mathematical treatment. He emphasises Oppenheimer¡¯s achievement in founding an American school of theoretical physics in California, even though his own contributions to quantum theory and, later, particle physics never quite matched those of the greatest. And Monk highlights pioneering pre-war work on neutron stars and their collapse into black holes that might have earned a Nobel prize if Oppenheimer had lived to see the identification of actual neutron stars in the late 1960s.

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The book also goes into serious detail about the oft-recounted technical challenges of making the first fission and fusion bombs, and deals manfully with the confusions in particle physics in the 1950s, when ¡°elementary¡± particles were proliferating in bewildering fashion. By then, though, Oppenheimer was more of an informed spectator than a player.

More dramatic, of course, was his departure from the centre of power. While Monk¡¯s treatment deals so thoroughly (and usually clearly) with the essential technicalities, the arc of Oppenheimer¡¯s involvement in affairs of state loses none of its narrative pull. The unexpected ascent of a communist fellow traveller to the post of scientific director of the Manhattan Project is followed by his continuing powerful influence as adviser to the newly formed US Atomic Energy Commission. Then, however, comes loss of his security clearance after a hearing orchestrated by a vengeful Lewis Strauss, AEC chairman, and one of the many people whom the quick-minded Oppenheimer had treated with something like contempt when they disagreed.

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As show trials go, the hearing was humane. Oppenheimer¡¯s term as adviser was due to end the day after it finished in 1954. He retreated painfully, but to his day job as director of the Institute for Advanced Study at Princeton University rather than the gulag. His life after the hearing was uneventful, but only by his own heroic standards. He continued to converse with the great, travel the world, and write and lecture on physics, science, society and politics until his death in 1967.

One of his late lecture themes, drawn out in Monk¡¯s final chapter, was the need for everyone to make a moral reckoning with the evil in themselves. The prescription gains power from the terrifying momentum of a nuclear arms race between Cold War superstates. But by this point the reader understands that Oppenheimer had wrestled all his life with lesser evils. His combination of intellectual brilliance and emotional illiteracy, vanity and insecurity led him to do and say many things best described as bizarre. How many of the ones he himself related to friends were actually true remains hard to decide. Did he really once try to drop a suitcase on the head of a woman he had just attempted to embrace on a train? Who knows? Did he really leave a poisoned apple on his tutor Patrick Blackett¡¯s desk at the University of Cambridge while in the throes of a postdoctoral breakdown triggered by his incompetence in the lab? Monk leans towards believing that he did, but even if we credit the testimony of the friend Oppenheimer told about the deed in most detail, can we trust the man himself?

Given Oppenheimer¡¯s propensity for myth-making and, when under pressure, making up stories that would later unravel, the answer is surely ¡°no¡±. In that sense, although there is no evidence of any security breaches and a mountain of evidence that his devotion to the US was second to none, the AEC verdict seems inescapable.

In setting the shifting shapes of Oppenheimer in context, Monk goes into generous detail about his background as the son of newly affluent, unreligious German Jews, educated in a school run by the secular Ethical Culture Society. In fact, he goes into more than usual detail about most everything. His dissection of Oppenheimer¡¯s often bewildering conduct is patiently exhaustive, endlessly judicious. He has mined anew the 296 boxes of Oppenheimer¡¯s own papers despite finding them curiously unrevealing, read everything Oppenheimer himself read or may have read, and pored over the mass of hearing transcripts, FBI interrogations and wiretaps, parts of which have already had as much critical attention as a Hamlet soliloquy. Although Monk aspires to complete understanding, he does not hesitate to own up when it eludes him. The word ¡°enigmatic¡± attaches to the subject no less often here than in other books about the man. A characteristic paragraph begins: ¡°As usual, Oppenheimer¡¯s behaviour was ambiguous and difficult to interpret¡±, followed by a catalogue of possible readings and a persuasively probabilistic conclusion.

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All this is not, as fellow biographer Richard Holmes suggests in a slightly surprising blurb, a book that explores ¡°new boundaries in the writing of biography itself¡±. Charles Thorpe¡¯s socio-history of Oppenheimer¡¯s career in science, politics and science politics in Oppenheimer: The Tragic Intellect (2006) does more in that direction but with the trade-off that it deals mainly with the 1940s and 1950s. Monk, in contrast, simply does conventional biography about as well as it can be done. Is this impressive effort the last word on Oppenheimer? His enduring elusiveness and symbolic embodiment of the anxieties of the age of weapons of mass destruction means that it is almost certainly not. Is it now the best place to begin taking the measure of the man? Absolutely.

The Author

Professor of philosophy at the University of Southampton, Ray Monk was born in Munich, ¡°then in the American-occupied sector of Germany, so I have three birth certificates - British, German and American. My father was in the British Army, in the Education Corps, teaching maths and science to a group of signallers who were based on the Austrian border, trying to listen to the Russians.¡±

He has lived in Southampton for 22 years (¡°it took a long time for me to warm to it but now I think of it as home¡±).

He lives ¡°with my partner Jenny and two of our children, Zala and Myron; our other two children, Danika and Zeno, are both at university. We have two cats, Spider and Ziggy.¡±

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Monk recalls: ¡°When I was quite young I used to think a lot about infinity. When I was a sixth-former, my English teacher lent me Plato¡¯s Symposium, which was the first philosophical text I read. Soon after, I became fascinated by Wittgenstein, and my brother bought me Philosophical Investigations for Christmas when I was 17. I still use that copy, which is now very worn.¡± He adds that he became ¡°utterly obsessed¡± with philosophy as an undergraduate at the University of York.

Of the eminent figures whose biographies he has written, he finds Bertrand Russell ¡°the most difficult, mainly because he left such a trail of emotional destruction in his wake. Wittgenstein is the one I feel closest to intellectually, emotionally and spiritually. Oppenheimer I find an endlessly fascinating enigma: breathtakingly intelligent across an amazing range of subjects but capable of astonishing stupidity.¡±

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In his spare time, Monk says, ¡°I play the guitar very badly, and also the ukulele, which has the great merit that no one can tell if you¡¯re playing it badly or not.¡±