In 1992, Tesauro completed TD-Gammon, which combined a form of unsupervised learning with the human-designed input features of Neurogammon, and played at the level of a world-class human tournament player.
Unlike previous neural-net backgammon programs such as Neurogammon (also written by Tesauro), where an expert trained the program by supplying the "correct" evaluation of each position, TD-Gammon was at first programmed "knowledge-free".