Early life

Larsen, who was born in Tilsted, near Thisted in Denmark, and was educated at Aalborg Cathedral School, represented Denmark twice in the World Junior Championship, in 1951 at Birmingham (placing fifth), and 1953 at Copenhagen (placing eighth). He never graduated in Civil Engineering, but decided to become a chess professional. He became an International Master at the age of 19 in 1954, from his bronze-medal performance on board one at the Amsterdam Olympiad. He won his first of six Danish Championships in 1954, and repeated in 1955, 1956, 1959, 1963, and 1964.

Larsen defeated Friðrik Ólafsson in an exhibition match at Oslo 1955 by 4½—3½. He won at Copenhagen 1956 with 8/9.

Young Grandmaster

Larsen became an International Grandmaster in 1956 with his gold-medal performance on board one at the Moscow Olympiad. He tied for 1st—2nd places at Hastings 1956—57 on 6½/9 with Svetozar Gligori?. At Dallas 1957, he scored 7½/14 for a shared 3rd—4th place; the winners were Gligori? and Samuel Reshevsky.

At the 1957 Wageningen Zonal, he tied for 3rd—4th places, along with Jan Hein Donner, with 12½/17; there were only three qualifying berths, so the two players had to dispute a playoff match. Larsen won by 3—1 over Donner at The Hague 1958 to qualify for his first Interzonal, at Portoro? 1958. Larsen could score only 8½/20 for 16th place, and was not close to qualifying. But he scored his first major individual international success by winning Mar del Plata 1958 with 12/15, ahead of William Lombardy, Erich Eliskases, Oscar Panno, and Herman Pilnik.

Larsen went into a slump beginning with the 1958 Interzonal. He tied 5th—6th in a powerful field at Zurich 1959 with 9½/15, behind winner Mikhail Tal, Gligori?, Paul Keres, and Bobby Fischer. But Larsen placed only 4th in a middle-range field at the 1960 Berg en Dal Zonal 1960 with 5½/9, and did not advance to the Interzonal. He recovered by sharing 1st—2nd places at Beverwijk 1961 on 7½/9 with Borislav Ivkov. At Zurich 1961, he tied for 6th—7th places with 6/11, as Keres won ahead of Tigran Petrosian. At Moscow 1962, he shared 7th—11th places with 7½/15 (Yuri Averbakh won).

Challenging for the World title

Around this time Larsen diversified his style, switching over to risky and unusual openings in some of his games, to try to throw his opponents off balance; this led to the recovery of his form and further development of his chess. He finished 2nd at the 1963 Halle Zonal with 13/19, behind winner Lajos Portisch, to advance to the Interzonal the next year. At Belgrade 1964, he shared 5th—6th places with 10/17 (Boris Spassky won). He tied for 5th—7th places at Beverwijk 1964 on 9½/15; Keres and Nei won. Larsen's unusual openings were on full display at the 1964 Amsterdam Interzonal, where he shared the 1st—4th places on 17/23 with Boris Spassky, Mikhail Tal, and Vasily Smyslov, advancing as a Candidate.

In the 1965 Candidates' matches, he first defeated Borislav Ivkov at Bled by 5½—2½, but lost in the semi-final, also at Bled by 4½—5½ to former world champion Mikhail Tal. He won a playoff match for alternates, an eventual third-place Candidates' position, against Efim Geller by 5—4 at Copenhagen 1966. In 1967 he won the Sousse Interzonal after Fischer withdrew, then won his first-round match against Lajos Portisch by 5½—4½ at Porec 1968. In Malmö, however, he lost the semi-final by 2½—5½ to Boris Spassky, who went on to win the title.

In 1970 he shared 2nd in the Palma de Mallorca Interzonal, on 15/23, behind Bobby Fischer. He reached his top rank in the Elo rating system at the start of 1971, equal third in the world (with Korchnoi, behind Fischer and Spassky) with a rating of 2660. He then defeated Wolfgang Uhlmann by 5½—3½ at Las Palmas 1971. But then he lost the semi-final 0—6 at Denver to Fischer, who also went on to win the title.

Larsen later claimed in a Kasparov.com interview (1998) that his one-sided loss to Fischer was due in part to his condition during the match: "The organizers chose the wrong time for this match. I was languid with the heat and Fischer was better prepared for such exceptional circumstances... I saw chess pieces through a mist and, thus, my level of playing was not good."

In 1973 he failed to advance from the Leningrad Interzonal; he tied for 5th—6th places with 10/17, with Anatoly Karpov and Viktor Korchnoi winning. In 1976 he won the Biel Interzonal, but lost his 1977 Candidates' match, a rematch of their 1968 encounter, to Lajos Portisch by 3½—6½ at Rotterdam. In the Riga Interzonal of 1979, Larsen scored 10/17 for 7th place, and did not advance.

Tournament dominance 1965—1973

Starting in the mid-1960s, Larsen enjoyed a very successful run in major tournaments around the world, and he and Fischer became the two strongest players outside the Soviet Union. Larsen played in a lot of strong events, at least as many as any other top player, and repeatedly finished ahead of the top Soviet players. He won at Le Havre 1966 with 9/11, ahead of Lev Polugaevsky. At Santa Monica 1966, he placed third with 10/18, behind Spassky and Fischer. He won at Havana 1967 with a powerful 15/19, ahead of a strong group which included Mark Taimanov, Smyslov, Polugaevsky, Gligoric, and Miroslav Filip. He shared 2nd—3rd places at Dundee 1967 with 5½/8, behind Gligoric. At Beverwijk 1967, he was 4th with 8½/15 (Spassky won). At Monte Carlo 1967, he shared 3rd—4th with 6/9, behind Fischer and Efim Geller. He shared 1st—2nd at Winnipeg 1967 with 6/9, along with Klaus Darga, ahead of Spassky and Keres. He won at Palma de Mallorca 1967 with 13/17, ahead of Smyslov, Mikhail Botvinnik, Portisch, Gligoric, and Borislav Ivkov. He was awarded the first Chess Oscar in 1967.

Somewhat unusual for the late 1960s, Larsen, as one of the world's top players, often entered large Open tournaments run on the Swiss system, and had plenty of success. He won the Canadian Open Chess Championships at Toronto 1968 and St. John's 1970. He also won the U.S. Open Chess Championships at Aspen 1968 and Boston 1970.

Larsen shared 2nd—3rd places at Palma de Mallorca 1968 with 13/17, along with Spassky; Viktor Korchnoi won. Larsen won at Monte Carlo 1968 with 9½/13, ahead of Botvinnik, Smyslov, Vlastimil Hort, Robert Byrne, Portisch, and Pal Benko. He defeated Heikki Westerinen by 6—2 in a 1969 exhibition match at Helsinki. In a playoff match for third place in the Candidates Tournament, he defeated Mikhail Tal at Eersel 1969 by 5½—2½ in a rematch of their 1965 encounter. He won at Palma de Mallorca 1969 with 12/17 ahead of Petrosian, Korchnoi, Hort, and Spassky. There was a further victory at Buesum 1969 with 11/15 ahead of Polugaevsky. At San Juan 1969, he scored 9/15 for a shared 6th—7th place (Spassky won).

Larsen won at Lugano 1970 with 9½/14, ahead of Olafsson. In the USSR vs Rest of the World match at Belgrade 1970, he played first board for the World side, ahead of Fischer, and scored 2½/4 against Spassky and Leonid Stein. At Leiden 1970, he shared 3rd—4th places with 5½/12, (Spassky won). He defeated Lubomir Kavalek in a 1970 exhibition match at Solingen by 6—2. He won at Vinkovci 1970 with 1½/15, ahead of David Bronstein, Hort, and Gligoric. At Palma de Mallorca 1970, he shared 6th—7th places with 9/15 (Panno and Ljubomir Ljubojevic were joint winners). Larsen shared 8th—9th places at San Antonio 1972 on 8½/15 (Portisch, Petrosian, and Anatoly Karpov triumphed). He won at Teesside 1972 with 11/15, ahead of Ljubojevic and Portisch. At Las Palmas 1972, he shared 2nd—3rd places on 11/15 (Portisch won).

Larsen won at Hastings 1972—73 on 11½/15, ahead of Wolfgang Uhlmann. At Bauang 1973, he scored 6/9 for 4th place (Kavalek won). Larsen won at Grenaa 1973 in the Nordic Championship with 8½/10. He won again at Manila 1973 with 12½/15, ahead of Ljubojevic and Kavalek.

Olympiad performances

He represented Denmark six times in Olympiad play, always on first board, and compiled an aggregate score of 75/109 (+61 =28 −20), for 68.8%, according to olimpbase.org. He always played a very high number of games, almost all of the rounds, and won three board medals, one gold and two bronze.

• Amsterdam 1954, board one, 13½/19 (+11 =5 −3), board bronze medal;
• Moscow 1956, board one, 14/18 (+11 =6 −1), board gold medal;
• Munich 1958, board one, 13/19 (+11 =4 −4);
• Havana 1966, board one, 11/18 (+9 =4 −5);
• Lugano 1968, board one, 10½/18 (+8 =5 −5);
• Siegen 1970, board one, 13/17 (+11 =4 −2), board bronze medal.

Later career

In 1988 he lost a game to Deep Thought in the Software Toolworks Championship, becoming the first Grandmaster and the player with the highest Elo rating (by then 2560) to be defeated by a computer in tournament play.

Larsen continued to play occasionally in tournaments, although he was becoming older and his health was failing. In 1999 he finished 7th of 10 in the Danish Championship, but in the 2000 event he was forced to withdraw when he became seriously ill with an edema, requiring brain surgery. Since then he only played a few tournaments in Buenos Aires. He was 4th in the 2002 Najdorf Memorial knock-out. In the April 2009 FIDE list, he had an Elo rating of 2415.

In his time, he defeated the seven World Champions who held the title from 1948 to 1985. He won games against Mikhail Botvinnik, Vasily Smyslov, Mikhail Tal, Tigran Petrosian, Boris Spassky, Bobby Fischer, and Anatoly Karpov.

He died in Buenos Aires in 2010. According to the English Chess Federation Newsletter, "His health had been poor for some considerabletime and he had been virtually inactive foryears".

Larsen was known as a deep thinking and highly imaginative player, more willing to try unorthodox ideas and to take risks than most of his peers. This aspect of his play could even manifest itself in his choice of opening. "He is a firm believer in the value of surprise. Consequently, he often resorts to dubious variations in various openings. He also likes to complicate positions even though it may involve considerable risk. He has a great deal of confidence in his game and fears no one. His unique style has proven extremely effective against relatively weak opponents but has not been too successful against top-notchers."

He was one of the very few modern Grandmasters to have employed Bird's Opening (1.f4) with any regularity, and had a long-term association with the move 1.b3, a system commonly known as Larsen's Opening or the Nimzo-Larsen Attack in his (and Aron Nimzowitsch's) honor. He played the Dutch Defence with success at a time when the opening was rarely seen at the top level. He revived the almost dormant Bishop's Opening (1.e4 e5 2.Bc4) with success in 1964 and explored new ways for Black to seek activity in the Philidor Defence (1.e4 e5 2.Nf3 d6). He was also the first top player to successfully use the Grand Prix Attack against the Sicilian Defence (1.e4 c5 2.f4), spurring a sudden and sustained gain in its popularity. In the mid-1960s, he showed surprising faith in Alekhine's Defence (1.e4 Nf6) and even employed it on important occasions. He played the rare Scandinavian Defence 1.e4 d5 to defeat World Champion Anatoly Karpov in 1979, sparking renewed interest in that variation. A favorite line in the Caro-Kann Defence (1.e4 c6 2.d4 d5 3.Nc3 dxe4 4.Nxe4 Nf6 5.Nxf6+ gxf6) is co-named for him and David Bronstein; the idea is to accept a weakness to the Black pawn structure in exchange for an unbalancing of the position and retaining the bishop pair.

The Grünfeld Defence (1.d4 Nf6 2.c4 g6 3.Nc3 d5) was another opening that became a frequent choice of Larsen with the Black pieces and similarly, he placed considerable reliance on Grunfeld-Indian systems as White. This led him to co-author a groundbreaking 1979 book (with Steffen Zeuthen) on this opening and similar structures (ZOOM 001...Zero Hour for Operative Opening Models). His book of 50 Selected Games (1968) is renowned for its pithy annotations which delve into chess psychology and the effective use of rare openings.

Larsen is respected as an excellent writer who reaches out to his readers; he was one of seven top Grandmasters who wrote fine chapters for the 1974 book How to Open a Chess Game. He edited the tournament book for San Antonio 1972.