Alan Turing was lived June 23, 1912 - June 7, 1954. Alan Turing is famous for the creating of his theoretical device, called the Turing machine . The machine was a response to a famous mathematical problem. The problem was if there was algorithm that always produced the correct response if given an input statement. Turing's machine had a memory, a reading and writing system, variables, and rules. The computers that we have now are examples of real Turing machines, also known as Turing complete machines.
Another thing that Alan Turing is famous for that has become a little more relevant recently is the Turing test. The Turing test is a way to determine if artificial intelligence can actually mimic humans. How the test works is that there is a human evaluator who looks over a text conversation between a human and artificial intelligence. If the evaluator can not determine which communicator is human and which is AI, then the artificial intelligence can mimic human speech. The test was created in 1950, and while it is an interesting question, artificial intelligence is getting more advanced and there isn't much of a need for the test anymore.
Turing is also widely regarded for his work decoding German enigma machines. These machines were ciphers, a type of encoding words, which the Germans used to communicate in World War II. Turing developed machines called bombes that would go through the possible combinations of ciphers and find the correct one.
CS department website