Tigran Petrosian (June 17, 1929 – August 13, 1984) was World Chess Champion from 1963 to 1969. He was nicknamed "Iron Tigran" due to his playing style because of his almost impenetrable defence, which emphasized safety above all else. He won the world championship in 1963 (against Botvinnik), successfully defended it in 1966 (against Spassky), and lost it in 1969 (to Spassky). 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. Source: Tigran Petrosian's Chess Biography on Wikipedia.