sentences:  He was a Candidate for the World Championship on eight occasions (1953, 1956, 1959, 1962, 1971, 1974, 1977 and 1980), won the world championship in 1963 (against Botvinnik) and 1966 (against Spassky), thus he was the defending World Champion or a World Champion candidate in ten consecutive three-year cycles.He won the Soviet Championship four times (1959, 1961, 1969, and 1975).He was arguably the hardest player to beat in the history of chess.