Alan Turing (1912 - 1954) was a British mathematician, logician, and cryptographer considered by many to be the father of computer science. His contributions to breaking the German Nazi Enigma code during WWII were considered pivotal to the Allied war effort. Alan Turing formulated multiple ideas that now lie at the foundations of computer science and computability theory, such as the idea of a Turing machine or the Church-Turing thesis.
A Turing machine is a simple mathematical construct that can be imagined as a recordable tape of infinite length coupled to a mechanical unit with read/write capability. The unit can perform only three actions; read a bit of the tape and return the result; write a bit on the tape; or erase a preexisting bit. Turing's Church-Turing thesis, formulated with Alonzo Church, states that such a Turing machine can theoretically compute any algorithm given enough time and storage space. It also states that any practical computing model must be a type of Turing machine. By extension, this means that the human brain can be defined as a Turing machine, because it processes information in the only way that information can be processed; by reading, writing, and manipulating bits of memory.
The Church-Turing thesis also claims that any algorithm can be run on anything that qualifies as a Turing machine. Turing helped formulate the original definition of an algorithm, which is roughly as follows: 1) an algorithm will consist of a finite set of precise instructions to be executed; 2) be computable in a finite number of steps (the inability of a program to determine whether or not it can be executed in a finite number of steps is called "the halting problem"); 3) be computable in principle with only a pen, paper, and infinite time; 4) require no background information to execute, that is, be self-contained.
Alan Turing was educated at Cambridge and Princeton throughout the 30s. In 1936, Turing published a very influential paper, On computable numbers, with an application to the Entscheidungsproblem, answering an open question posed by Kurt Goedel in 1931, which showed that there is no algorithmic way to determine whether a given first-order statement in symbolic logic is universally valid. In 1938, Alan Turing earned his PhD from Princeton under Alonzo Church.
Alan Turing spent his post-war years working on some of the first reprogrammable digital computers, producing one of the first designs in 1946. He also addressed the problem of artificial intelligence, formulating the Turing Test, a test for determining whether or not a machine deserves to be called conscious and intelligent. In the Turing Test, a human being types words into a keyboard to communicate with two hidden persons, one an actual human being, the other an AI. If the human being cannot distinguish which communicant is the human and which is the AI, the AI is said to have passed the Turing Test. Some futurists, such as National Medal of Technology winner Ray Kurzweil, have suggested that we will have a Turing Test-passing computer before 2030.
Alan Turing died in 1954, due to a cyanide-laced apple. His death is said to be a suicide, a result of being prosecuted for homosexuality and being forced to take hormones by the government.