Alan Turing: the enigma

This biography of Alan Turing is one of the best biographies of any type I've read. Andrew Hodges explores the known facts of Turing's life, goes into the details of his mathematical, philosophical and scientific work, and tells a convincing story about Turing's inner life based on papers left behind and testimony from friends and associates. He also does a good job of explaining the distinct way that the time in which Turing lived shaped the story of his life. It's a weighty, substantial book, but very readable even for someone (me) who isn't particularly strong in math.

This is also the book which the movie The Imitation Game credits as its inspiration. The movie oversimplifies the story (necessarily?) in places, but also takes liberties with the facts (annoyingly). See the movie as a fairy tale, but read the book for a real, complex, and completely fascinating interpretation of Turing's story.