Alan Turing's work could be said to have begun the digital revolution. Although others around the world, such as the American, Alonzo Church, had done some work, it was Alan Turing who envisaged and designed a Machine that could be given a rule set upon which it would base its actions and could therefore be programmed to solve an infinite number of problems: in fact, any problem for which there was a solution(basically a modern computer). It was Alan Turing who was instrumental in the development of the Bombe at Bletchley Park and it was Alan Turing whose ground-breaking ideas about Artificial Intelligence (AI) really pushed the boundaries of mathematical thinking at that time.
When Time magazine published its list of the 100 most important people of the twentieth century, they included Alan Turing in that list and said of him:
"The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine."
Of his many important papers, the most well known are:
On Computable Numbers, with an Application to the Entscheidungsproblem (28 May 1936) in which Alan Turing first outlined his idea of a Universal Machine which could tackle any mathematical problem and which became known as the Turing Machine.
Computing Machinery and Intelligence (1950) in which Alan Turing first proposes the Turing test to decide whether a computer can be called intelligent or not.