Tigran Vardani Petrosian (Armenian: Տիգրան Վարդանի Պետրոսյան; Russian: Тигран Вартанович Петросян; 17 June 1929 – 13 August 1984) was a Soviet-Armenian chess grandmaster. The ninth World Chess Champion from 1963 to 1969, he was nicknamed "Iron Tigran" due to his almost-impenetrable defensive playing style, which emphasized safety above all else. Petrosian is often credited with popularizing chess in Armenia.

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).

Petrosian was born to Armenian parents on 17 June 1929, in Tbilisi, Georgian SSR (present-day Georgia). As a young boy, Petrosian was an excellent student and enjoyed studying, as did his brother Hmayak and sister Vartoosh. He learned to play chess at the age of eight, though his illiterate father Vartan encouraged him to continue studying, as he thought chess was unlikely to bring his son any success as a career. Petrosian was orphaned during World War II and was forced to sweep streets to earn a living. Around this time, his hearing began to deteriorate, a problem that continued to affect him throughout his life. In a 1969 interview with Time magazine, he recalled:

I started sweeping streets in the middle of the winter and it was horrible. Of course there were no machines then, so we had to do everything by hand. Some of the older men helped me out. I was a weak boy. And I was ashamed of being a street sweeper—that's natural, I suppose. It wasn't so bad in the early morning when the streets were empty, but when it got light and the crowds came out I really hated it. I got sick and missed a year in school. We had a babushka, a sister of my father, and she really saved me. She gave me bread to eat when I was sick and hungry. That's when this trouble with my hearing started. I don't remember how it all happened. Things aren't very clear from that time.

Petrosian used his rations to buy Chess Praxis by Danish grandmaster Aron Nimzowitsch, the book which Petrosian later stated had the greatest influence on him as a chess player. He also purchased The Art of Sacrifice in Chess by Rudolf Spielmann. The other player to have had an early effect on Petrosian's chess was José Raúl Capablanca. At the age of 12 he began training at the Tiflis Palace of Pioneers under the tutelage of Archil Ebralidze. Ebralidze was a supporter of Nimzowitsch and Capablanca, and his scientific approach to chess discouraged wild tactics and dubious combinations. As a result, Petrosian developed a repertoire of solid positional openings, such as the Caro–Kann Defence. After training at the Palace of Pioneers for just one year, he defeated visiting Soviet grandmaster Salo Flohr at a simultaneous exhibition.

By 1946, Petrosian had earned the title of Candidate Master. Also that year he drew against Grandmaster Paul Keres at the Georgian Chess Championship, then moved to Yerevan where he won the Armenian Chess Championship and the USSR Junior Chess Championship. Petrosian earned the title of Master during the 1947 USSR Chess Championship, though he failed to qualify for the finals. He set about improving his game by studying Nimzowitsch's My System and by moving to Moscow to seek greater competition.

After moving to Moscow in 1949, Petrosian's career as a chess player advanced rapidly and his results in Soviet events steadily improved. He placed second in the 1951 Soviet Championship, thereby earning the title of international master. It was in this tournament that Petrosian faced world champion Botvinnik for the first time. Playing White, after obtaining a slightly inferior position from the opening, he defended through two adjournments and eleven total hours of play to obtain a draw. Petrosian's result in this event qualified him for the Interzonal the following year in Stockholm. He earned the title of Grandmaster by coming in second in the Stockholm tournament, and qualified for the 1953 Candidates Tournament.

Petrosian placed fifth in the 1953 Candidates Tournament, a result which marked the beginning of a stagnant period in his career. He seemed content drawing against weaker players and maintaining his title of Grandmaster rather than improving his chess or making an attempt at becoming World Champion. This attitude was illustrated by his result in the 1955 USSR Championship: out of 19 games played, Petrosian was undefeated, but won only four games and drew the rest, with each of the draws lasting twenty moves or fewer. Although his consistent playing ensured decent tournament results, it was looked down upon by the public and by Soviet chess media and authorities. Near the end of the event, journalist Vasily Panov wrote the following comment about the tournament contenders: "Real chances of victory, besides Botvinnik and Smyslov, up to round 15, are held by Geller, Spassky and Taimanov. I deliberately exclude Petrosian from the group, since from the very first rounds the latter has made it clear that he is playing for an easier, but also honourable conquest—a place in the interzonal quartet."