Petrosian was a Candidate for the World Chess Championship on eight occasions (1953, 1956, 1959, 1962, 1971, 1974, 1977 and 1980). He won the World Championship in 1963 (against Mikhail Botvinnik), successfully defended it in 1966 (against Boris Spassky), and lost it to Spassky in 1969. Thus he was the defending World Champion or a World Championship Candidate in ten consecutive three-year cycles. He won the Soviet Championship four times (1959, 1961, 1969, and 1975).