Submitted by University of Toronto professor Anatol Rapoport, the program was called Tit for Tat. The strategy always began with cooperating, and then simply did what the other player did on the previous move, cooperating if the other cooperated, defecting if the other defected. It did not hold a grudge: if its opponent began to cooperate again after defecting, Tit for Tat would also return to cooperation.
