Without this book, the real Alan Turing might fade into obscurity or at least the easy caricature of an eccentric British mathematician. And to the relief of many, because Turing was a difficult person: an unapologetic homosexual in post-victorian england; ground-breaking mathematician; utterly indifferent to social conventions; arrogantly original (working from first principles, ignoring precedents); with no respect for professional boundaries (a 'pure' mathematician who taught himself engineering and electronics).
His best-known work is his 1936 'Computable Numbers' paper, defining a self-modifying, stored-program machine. He used these ideas to help build code-breaking methods and machinery at Bletchley Park, England's WWII electronic intelligence center. This work, much still classified today, led directly to the construction of the world's first stored-program, self-modifying computer, in 1948.
Computers were always symbol-manipulators to Alan, not 'number crunchers', the predominant view even to von Neumann, and into the 60's and 70's. He designed many basic software concepts (interpreter, floating point), most of which were ignored (he umm wasn't exactly good at promoting his ideas). By 1948 Alan had moved on to studying human and machine intelligence, as a user of computers, again with his lack of social niceties and radical thinking, some of his ideas were baffling or embarrassing until 'rediscovered' decades later as brilliant insights into intelligence. His 'Turing test' of intelligence dates from this period, and is still widely misunderstood.
Poor Alan; his refusal to deceive himself or others and "go along" with the conventions of the time regarding sexuality caused him (and other homosexuals then) great problems; early Cold War England was not a good time to be gay, or a misfit, especially one with deep knowledge of war-time secrecy (he was technical crypto liason to the U.S., and one of the few with broad knowledge of operations at Bletchley, since he defined so much of it, in a time of extreme compartmentalization). His sexual escapades eventually got him in trouble, and his increasing isolation and the fact that he simply couldn't acknowledge some of his life's work due to secrecy, probably influenced his suicide at the age of 42.
I first discovered Turing-the-person in A HISTORY OF COMPUTING IN THE 20TH CENTURY (Metropolis, Howlett, Gian-Carlo Rota; Acedemic Press, 1980), where I.J. Good wrote, "we didn't know he was a homosexual until after the war... if the security people had found out [and removed him]... we might have lost the war". This led me to look for books on Turing, and then the Hodges book magically appeared on the shelf.
I am grateful that Hodges researched his life as well as his work, as far as the data allows. Knowing the whole is always important, but I think critical in Alan Turing's life.
My only complaint with the book is that it makes a number of assumptions or implications that seem to require knowledge of British culture, both contemporary and of the period, which I still didn't pick up on a re-reading. But it barely detracts from the book.
Clearly, I rate this one of the most important books I've ever read.