The Turing Test
In 1950, Alan Turing proposed the Turing Test as a way to determine if a computer program could think like a human being. He proposed that a judge talk to a computer and man over telephone lines, and see, if by conversation alone, he could choose the human. If he was "fooled" by the computer program, then it was truly Artificially Intelligent.
Turing's 1950 paper in Mind, Computing Machinery and Intelligence, has become one of the most cited in philosophical literature, and heads the list in David Chalmers' bibliography of the philosophy of Artificial Intelligence.