Alan Mathison Turing was born on 23 June 1912 in a nursing home in Paddington, London. He was the second child of civil servant Julius Mathison Turing and his wife Ethel Sara Turing. His early childhood was defined by his parents' absence. Alan and his elder brother John lived with foster families until 1926, because of his parent's constant absence due to his father's job in Madras, India.
Turing's formal eduction began at Hazlehurst Preparatory School where he was apparently an average pupil, though often preoccupied with his own ideas. In 1926 he passed his Common Entrance Examination and began attending Sherborne School despite the General Strike of that year, which meant he had to cycle 60 miles a day to school and back. He had a hard time fitting into the public school way of life, but his close friendship with Christopher Morcom seemed to help, and for the first time Turing seemed to have found someone he could share his thought and ideas with.
All this was not to last, as tragedy struck in February 1930. Morcom caught tuberculosis and died, kick-starting a passion for understanding the processes behind human thought in Turing, and a conviction that he must now do what Morcom could not, which apparently sustained him through the crisis. His preference for science over all other subjects, which had been made even stronger than before by his friend's death, often found him at odds with the schools headmaster, and almost led to an abrupt termination of Alan's academic career as, despite his apparently excellent grasp on physics, he was almost denied the opportunity to take his exams as it was feared that he would embarrass the school by failing them.
This never happened, and in 1931 Turing won a scholarship to King's College, Cambridge and began his undergraduate life studying mathematics, a subject in which he earned his degree in 1934. His time at Kings seems to have been a happy if confused one, as it was at about this time he started to become conscious of his homosexuality. His personal life remained confused, though, and he had a hard time making friends. His completion of his undergraduate course was followed by a Fellowship of King's College in 1935 and the Smith's Prize in 1936 for work on probability theory. This may have been the pinnacle of his career had it not been for his attendance at a lecture on mathematical logic given by M. H. A. Newman, a topologist, during which the mythical Entscheidungsproblem posed by Hilbert was mentioned, and piqued Turing's interest.
Unfortunately, a mere three months before the Turing published his paper, the American logician Alonzo Church produced his own solution to the problem, using the much more familiar lambda calculus method of mathematical logic and in doing so gaining much praise from mathematicians worldwide. This did not invalidate Turing's work though and the publication of his now famous paper On Computable Numbers, with an application to the Entscheidungsproblem contained a novel method of solving the problem by the use of a device known as a 'Turing Machine'.
In the beginning, the machine was just a thought experiment, designed to prove a very abstract mathematical theorem, but Turing realised the potentially awesome power of his idea. With a little extra work, Alan came up with the theory of the Universal Turing Machine, essentially a Turing Machine capable of carrying out the function of any of the infinite number of possible Turing Machines, and in doing so laid foundation of the modern theory of computation and computability.
At the time this was not recognised as the defining moment in computing that it is now, but one man who had seen a glimpse of the potential of the Universal Turing Machine was the acclaimed Hungarian-American mathematician, John von Neumann. He invited Turing to attend Princeton University as a graduate student and carry on his work. He arrived in September 1936 and spent much of his time making a cipher machine based on using electromagnetic relays to multiply binary numbers and the rest of it completing his Ph.D thesis on Ordinal Logic. After earning his doctorate in 1938, von Neumann offered Turing a temporary post at Princeton, but instead he chose to return to his alma mater to start investigating the possibility of making a machine to calculate the Riemann-Zeta function.
It was at about this time that Turing started to work part-time for the British cryptanalytic department, the so-called Government Code and Cypher School, previously a bastion of the arts, who were having immense problems breaking the German Enigma code. The major breakthrough in the cracking of the Enigma code came from work done by Polish mathematicians, who had also suggested that this work might be automated. Upon British declaration of war on 3 September 1939, Turing was stationed at the now famous Bletchley Park code-breaking 'factory', and was set to work creating a device to do this. The outcome of the project in which he was aided by another Cambridge mathematican, W. G. Welchman was known as a 'Bombe'. The success of the Turing-Welchman Bombe at deciphering Luftwaffe signals made the communications of the German air force virtually an open book.
Turing's attention then turned to the Enigma messages being sent by the German navy, which were more complex. He set up 'Hut 8' which concentrated on the use of complex statistical methods in an attempt to find a way of decrypting of naval and U-boat Enigma signals. The first success came in 1939 when the Naval messages were broken for the first time, but it took until 1941 for the method to become routine. A minor crisis occurred later on the 1st February 1942 when the U-Boat fleets changed the configuration of their Enigma machines, and included an extra rotor. This additional complexity in the encryption procedure effectively 'turned off the lights' in the Atlantic, and took until mid-1943 before reading them became possible again.
Whilst working in an official capacity on in 'Hut 8', Turing's friend, M. H. A. Newman, managed to gain him a place for him working with the telephone engineers who had been brought to Bletchley Park in an attempt to speed up the decryption of 'Fish' messages which were used to encode Adolf Hitler's strategic communications. The combination of electronic expertise, and Turing's ideas of computability gave rise to what is considered to be one of the first electronic computers - Colossus.
The success with Fish and Enigma led to Turing's briefly working on a voice encryption mechanism with his assistant Donald Bayley, at nearby Hanslope Park, and for this and his other wartime exploits he received an OBE, but had already been set thinking about an implementation of the Universal Turing Machine by the experience he gained whilst working at Bletchley Park. Yet again he had the misfortune of being 'gazumped' by the Americans, this time aided and abetted by his old friend John von Neumann and the EDVAC project. This time though things worked more to his advantage as the National Physical Laboratory in London set up a rival project, known as the Automatic Computing Engine or ACE.
Turing's design for ACE was formally approved in early 1946 and his dream of creating a machine that was able to able to switch at will from algebra to code-breaking, or from file handling to chess-playing. This project was doomed to fail though and the ACE was never built during Turing's time at the NPL. Turing blamed the lack of co-operative effort for the delay of the project and turned his back on the emerging science of computing, leaving other computer projects at Cambridge and also at Manchester to take over, the latter of these ultimately culminated in the Manchester Mark 1, arguably the world's first stored program computer.
Although never totally in 'the closet', Turing became more and more open about his sexuality and openly had a relationship with a mathematics student at King's College, Neville Johnson, upon his return to Cambridge. He also rekindled his interest in athletics and was only kept out of the 1948 Olympic squad by injury.
In May 1948, von Newmann offered Turing the post as Deputy Director of the computing laboratory at Manchester University, which he duly accepted. Most of his time was spent devising programmes to run on the engineers' machines, but he partly rediscovered his love of logic, implementing the Riemann-Zeta function, and checking Church's thesis on the the prototype computers in the laboratory, and his thoughts on the connections between machines and human thought in his paper Computing Machinery and Intelligence which appeared in the philosophical journal Mind in 1950. This paper also outlines the now famous experiment which tests for A.I, the Turing Test.
Turing's academic direction dramatically changed shortly afterward he was elected to Fellowship of the Royal Society in July 1951. He spent his time focusing on the underlying theories of growth and form in biology. He was particularly puzzled by the appearance of the Fibonacci numbers in plant leaf structures and from his studies on the development of pattern and form in living organisms he wrote a paper entitled The Chemical Basis of Morphogenesis which is now considered to be a founding paper of modern non-linear dynamical theory.
The Government's laws prohibiting homosexuality finally caught up with Turing on 31st March 1952, when he was arrested and came to trial after the police learned of his relationship with a young Manchester man whilst investigating a break in. His defence was that he saw nothing wrong with what he had done; but rather than sending him to prison, he was sentenced to take oestrogen injections for a year, which were intended to neutralise his libido. This alone was not a problem, but this conviction caused Turing to lose his security clearance, as since 1948, the conditions of the Cold War and the alliance with the USA, meant that known homosexuals were considered to be a risk to national security, and Alan was forced to resign from his work with the GCHQ, a cruel blow for the man who had revolutionised the way that intelligence data was analysed.
His body was found by his cleaner on 8 June 1954 in his house in Wilmslow, Cheshire. He had died the day before of cyanide poisoning, a half-eaten apple laced with the chemical beside his bed.
Sources include:
http://www.turing.org.uk/turing/scrapbook
http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Turing.html
http://www.turing.org.uk/turing/bio/