I read some of his 1984 book "Mathematical Methods in the Social and Behavioral Sciences" and it's a great book. There are not many people who have a strong and original mathematical mind and yet know how to apply it with wisdom, but Rapoport's reach and depth in the book is hugely impressive.
Rapoport was the author of Tit for Tat, the benevolent strategy for prisoner's dilemma that won the earliest tournaments conducted by Axelrod at Michigan.
Globe&Mail: That year also saw publication of political scientist Robert Axelrod's seminal book, The Evolution of Co-operation, which asked a simple, yet age-old, question: If living things evolve through competition, how can co-operation ever emerge? A computer tournament was organized to study the relationship of game theory to evolution -- a variation on the Prisoner's Dilemma. Entries came from the world's top theorists.
Dr. Rapoport entered a program he wrote called Tit-For-Tat, consisting of four lines of code. It was by far the simplest entry, and it won. Betraying the retributive implications of its name, the program opened by co-operating with its opponent. Thereafter, it played exactly as the other side had played in the preceding game. If the other side had defected, Tit-For-Tat also defected for that one game. If the other side had co-operated, it co-operated on the next round.
"In effect, Tit-For-Tat punished the other player for selfish behaviour and rewarded her for co-operative behaviour -- but the punishment lasted only as long as the selfish behaviour lasted," observed Metta Spencer, editor of Peace Magazine, on the occasion of Dr. Rapoport's 90th birthday. "This proved to be an exceptionally effective sanction, quickly showing the other side the advantages of co-operating. . . . It also set moral philosophers to proposing this as a workable principle to use in real life interactions."