Alan Turing was a brilliant mathematician who helped define the theoretical model of the computer as we know it today. Alan was a visionary, one of the few of his time who foresee the role computers would play for humanity in future. Alan was also the author of the earliest substantial work in the field of artificial intelligence when in 1935 he described an abstract computing machine consisting of a limitless memory and a scanner that moves back and forth through the memory, symbol by symbol, reading what it finds and writing further symbols. The actions of the scanner are dictated by a program of instructions that also is stored in the memory in the form of symbols marking the beginning of computer programs as we know them today and for this Turing is widely considered to be the father of computer science and artificial intelligence.

I believe it’s only fair we can Alan is one of the main fathers of the computers we all use today.

But to understand a bit more about this unique individual and his legacy, there’s a few interesting texts (apart from the usual wikipedia), like his biography or this one from BBC history on Alan Turing:

Alan Turing was born on 23 June, 1912, in London. His father was in the Indian Civil Service and Turing’s parents lived in India until his father’s retirement in 1926. Turing and his brother stayed with friends and relatives in England. Turing studied mathematics at Cambridge University, and subsequently taught there, working in the burgeoning world of quantum mechanics. It was at Cambridge that he developed the proof which states that automatic computation cannot solve all mathematical problems. This concept, also known as the Turing machine, is considered the basis for the modern theory of computation.
In 1936, Turing went to Princeton University in America, returning to England in 1938. He began to work secretly part-time for the British cryptanalytic department, the Government Code and Cypher School. On the outbreak of war he took up full-time work at its headquarters, Bletchley Park.
Here he played a vital role in deciphering the messages encrypted by the German Enigma machine, which provided vital intelligence for the Allies. He took the lead in a team that designed a machine known as a bombe that successfully decoded German messages. He became a well-known and rather eccentric figure at Bletchley.
After the war, Turing turned his thoughts to the development of a machine that would logically process information. He worked first for the National Physical Laboratory (1945-1948). His plans were dismissed by his colleagues and the lab lost out on being the first to design a digital computer. It is thought that Turing’s blueprint would have secured them the honour, as his machine was capable of computation speeds higher than the others. In 1949, he went to Manchester University where he directed the computing laboratory and developed a body of work that helped to form the basis for the field of artificial intelligence. In 1951 he was elected a fellow of the Royal Society.
In 1952, Turing was arrested and tried for homosexuality, then a criminal offence. To avoid prison, he accepted injections of oestrogen for a year, which were intended to neutralise his libido. In that era, homosexuals were considered a security risk as they were open to blackmail. Turing’s security clearance was withdrawn, meaning he could no longer work for GCHQ, the post-war successor to Bletchley Park.
He committed suicide on 7 June, 1954.

And since Alan wasn’t just a Mathematician, Nature is also running a special on his work.