Turing is often considered to be the father of modern computer science. Turing provided an influential formalisation of the concept of the algorithm and computation with the Turing machine. With the Turing test, he made a significant and characteristically provocative contribution to the debate regarding artificial intelligence: whether it will ever be possible to say that a machine is conscious and can think. He later worked at the National Physical Laboratory, creating one of the first designs for a stored-program computer, although it was never actually built. In 1948 he moved to the University of Manchester to work on the Manchester Mark I, then emerging as one of the world's earliest true computers.

During the Second World War Turing worked at Bletchley Park, Britain's codebreaking centre, and was for a time head of Hut 8, the section responsible for German naval cryptanalysis. He devised a number of techniques for breaking German ciphers, including the method of the bombe, an electromechanical machine that could find settings for the Enigma machine.

In 1952, Turing was convicted of "acts of gross indecency" after admitting to a sexual relationship with a man in Manchester. He was placed on probation and required to undergo estrogen therapy to achieve temporary chemical castration. His father, Julius Mathison Turing, was a member of the Indian Civil Service. Julius and wife Sara (née Stoney; 1881 – 1976, daughter of Edward Waller Stoney, chief engineer of the Madras Railways) wanted Alan to be brought up in England, so they returned to Maida Vale, London, where Alan Turing was born 23 June 1912, as recorded by a blue plaque on the outside of the building, now the Colonnade Hotel. He had an elder brother, John. His father's civil service commission was still active, and during Turing's childhood years his parents travelled between Guildford, England and India, leaving their two sons to stay with friends in England. Very early in life, Turing showed signs of the genius he was to display more prominently later.

His parents enrolled him at St Michael's, a day school, at the age of six. The headmistress recognised his genius early on, as did many of his subsequent educators. In 1926, at the age of 14, he went on to Sherborne School in Dorset. His first day of term coincided with General Strike in England, but so determined was he to attend his first day that he rode his bike unaccompanied more than 60 miles from Southampton to school, stopping overnight at an inn.

Turing's natural inclination toward mathematics and science did not earn him respect with the teachers at Sherborne, a famous and expensive public school, whose definition of education placed more emphasis on the classics. His headmaster wrote to his parents: "I hope he will not fall between two schools."