[3] Born in Leningrad, Soviet Union (USSR), Korchnoi defected to the Netherlands in 1976, and resided in Switzerland from 1978, becoming a Swiss citizen.

In 1978 and 1981, Korchnoi won consecutive Candidates cycles and qualified to challenge Karpov for the World Chess Championship, but lost both matches.

), a daughter of the Yiddish writer Hersh Azbel, was a pianist and alumna of Leningrad Conservatory of Music; his father, Lev Merkuryevich Korchnoi (1910–1941), was an engineer, who worked at a candy factory.

In 1943, he joined the chess club of the Leningrad Pioneer Palace, and was trained by Abram Model, Andrei Batuyev, and Vladimir Zak.

Korchnoi improved on the previous year's showing with his shared 2nd–3rd place in URS-ch21 at Kyiv 1954, on 13/19, as GM Yuri Averbakh won.

His complete Soviet international team play results follow: Korchnoi rose to prominence within the Soviet chess school system, where he competed against his contemporaries and future GM stars such as Mikhail Tal, Tigran Petrosian, and Boris Spassky, following in the path laid out by Mikhail Botvinnik.

[22] After his victory at Budapest 1961 (Géza Maróczy Memorial) with 11½/15 ahead of GMs David Bronstein and Miroslav Filip, each with 9½, Korchnoi was recognized as one of the world's best players.

[16] Korchnoi's results included two victories over Fischer, one a brilliant win employing the Pirc Defense with the black pieces.

He missed qualifying for the next world championship cycle, 1964–66, because of a poor showing at the 1964 Zonal tournament in Moscow, where he made 5½/12 for a shared 5th–6th place, so did not advance to the Interzonal.

[25] In the 1969 World Championship cycle, he tied for 3rd–5th places at the URS-ch34, held at Tbilisi 1966–67, with 12/20, and emerged from a three-way playoff, along with GM Aivars Gipslis, at Tallinn 1967, to the Interzonal, staged at Sousse, Tunisia, later that year.

The match, held in Moscow 1968, was close, but Korchnoi won by (+2−1=7), and moved on to face GM Boris Spassky in the Candidates' final.

Korchnoi, as the losing finalist, was exempt from qualifying for the 1972 World Chess Championship, and was seeded directly to the following Candidates' event.

[29] In 1972, Korchnoi appeared in the chess-themed Soviet film Grossmeister along with several other grandmasters; he played the role of the lead actor's trainer.

[30] In the 1975 World Championship cycle Korchnoi and Karpov, the newest star of Soviet chess, tied for first in the 1973 Leningrad Interzonal.

[32] With his victory over Petrosian, Korchnoi advanced to face Karpov in the Candidates' Final, the match to determine who would challenge reigning world champion Bobby Fischer in 1975.

By default, Karpov became the twelfth world champion in April 1975, when Fischer refused to defend his title because of disputed match conditions.

The ban against Korchnoi competing outside the USSR was lifted when he accompanied fellow veteran GMs Mark Taimanov and Bronstein to London to play a Scheveningen-style event (where each team member competes against only the other team's players) against three young British masters: Jonathan Mestel, Michael Stean and David S. Goodman.

[35] Korchnoi, in a 2006 lecture in London, mentioned that the breakthrough that allowed him to resume international appearances came when Anatoly Karpov inherited the World Championship title forfeited by Fischer.

He played a short match against GM Jan Timman – the strongest active non-Soviet player at that time – and comprehensively defeated him.

[37] Korchnoi began actual play by again vanquishing Petrosian, by (+2−1=9) in the quarter-final round at Il Ciocco, Italy, taking a clinching draw in a clearly favourable position in the final game.

[39] Ultimately, Korchnoi steeled himself and finally secured victory in the match by (+7−4=7) to emerge as the challenger to Karpov, having defeated three world-class Soviet contenders.

At Buenos Aires during July and August 1980, Korchnoi again triumphed by 7½ to 6½; the match was tied following the regulation ten games.

[citation needed] However, upon intervention by prominent British chess organizer GM Raymond Keene, who quickly stepped up to raise a large amount of sponsorship money to save the troubled matches, Korchnoi agreed to play Kasparov in London, which at the same time also hosted the Smyslov vs. Ribli match.

[50] In the 1988–90 cycle, he made the final 16 again, but was eliminated in the first round of Candidates' matches, held at Saint John, New Brunswick, Canada, losing to Iceland's GM Johann Hjartarson in extra games, by 4½ to 3½.

He frequently represented their Olympiad team on top board, beginning in 1978, even though his Elo rating was sometimes considerably below that of compatriot Vadim Milov, who appeared not to make himself available for selection.

In September 2006, Korchnoi won the 16th World Senior Chess Championship, held in Arvier (Valle d'Aosta, Italy), at age 75, with a 9–2 score.

[61] FIDE President Kirsan Ilyumzhinov said that Korchnoi "has contributed substantially to the popularisation of our sport and is considered rightly as one of the strongest and charismatic players in the entire history of world chess".

In the 1983 U.S. Open Chess Championship in Pasadena, California, Korchnoi was paired against GM Larry Christiansen who was late showing up to the game when his "old jalopy" car ran out of gas on the way to the event.

[64] Korchnoi never succeeded in becoming world chess champion, but many people consider him the strongest player never to have done so, a distinction also often attributed to Akiba Rubinstein and Paul Keres.

[71] Korchnoi defeated nine undisputed world champions (Botvinnik, Smyslov, Tal, Petrosian, Spassky, Fischer, Karpov, Kasparov and Carlsen), a record he shares with Paul Keres and Alexander Beliavsky.