Question: Who was the opponent of Viktor Korchnoi in the 1981 final match on the Candidates Tournament?
Context: Samuel "Sammy" Herman Reshevsky (born Szmul Rzeszewski; November 26, 1911 – April 4, 1992) was a Polish chess prodigy and later a leading American chess grandmaster.  He was never a full-time chess professional.  He was a strong contender for the World Chess Championship from the mid-1930s to the mid-1960s: he tied for third place in the 1948 World Chess Championship tournament, and tied for second in the 1953 Candidates Tournament.  He was an eight-time winner of the U.S. Chess Championship.  An outstanding match player throughout his career, Reshevsky excelled at positional play, and could be a brilliant tactician when required.  He took a long time over his opening moves, and often found himself in time pressure, but this sometimes unsettled his opponent more than it did Reshevsky. Georgy Konstantinovich Borisenko (May 25, 1922 in Chuhuiv, Ukraine—December 3, 2012 in Tashkent, Uzbekistan) was a Soviet correspondence chess grandmaster and chess theoretician.  Among the players he trained were Nona Gaprindashvili, Valentina Borisenko (who was also his wife), Viktor Korchnoi, Mark Taimanov, and Timur Gareyev.  He became a Russian Master of Sport in 1950 and a Russian Correspondence Grandmaster in 1966.  He won the USSR Correspondence Championship twice, in 1957 and 1962, and came in second in 1965.  One of his best-known games was played from 1960 to 1963 against Anatoly Rubezov, and is included in multiple anthologies of brilliant chess games.  In 1973, David Bronstein described Borisenko as "one of our greatest theoretical experts."  In Russia, the Breyer Variation of the Ruy Lopez is known as the "Borisenko-Furman" variation because Borisenko and Semyon Furman were central in bringing it into use in the 1950s.  Another line of the Closed Ruy Lopez is also named after him; specifically, the line in the Chigorin Variation which goes 9...Na5 10. Bc2 c5 11. d4 Nc6. Jóhann Hjartarson (born 8 February 1963) is a chess player from Iceland.  He earned the International Master title in 1984 and the Grandmaster title a year later.  Among his best international tournament results are shared first place at Reykjavík in 1984 and 1992, shared first at World Open 1991 in Philadelphia, equal third at Tilburg 1988 (+3−3=8) and sixth at Belgrade 1989 (+2−2=7).  In 1987 he finished equal first at the Interzonal tournament in Szirák, Hungary and qualified for the World Championship Candidates Tournament in 1988.  He defeated Viktor Korchnoi but lost to Karpov in the quarterfinals.  Jóhann competed in the FIDE world championship held with the knock-out format in 1998 and 2004. Viktor Lvovich Korchnoi (Russian: Ви́ктор Льво́вич Корчно́й ; ] ; 23 March 1931 – 6 June 2016) was a Soviet (until 1976) and Swiss (since 1994) chess grandmaster and writer.  He is considered one of the strongest players never to have become World Chess Champion. The major chess events of 1981 were the final match of the Candidates Tournament (between Viktor Korchnoi and Robert Hübner) and the second Karpov–Korchnoi World Chess Championship match. Chess is a musical with music by Benny Andersson and Björn Ulvaeus of the pop group ABBA, and with lyrics by Tim Rice.  The story involves a politically driven, Cold War-era chess tournament between two men—an American grandmaster and a Soviet grandmaster—and their fight over a woman who manages one and falls in love with the other.  Although the protagonists were not intended to represent any real individuals, the character of the American grandmaster (named Freddie Trumper in the stage version) was loosely based on Bobby Fischer, while elements of the story may have been inspired by the chess careers of Russian grandmasters Viktor Korchnoi and Anatoly Karpov. The Candidates Tournament is a chess tournament organized by FIDE, chess's international governing body, since 1950, as the final contest to determine the challenger for the World Chess Championship.  The winner of the Candidates earns the right to a match for the World Championship against the incumbent World Champion.  The last FIDE World Chess Candidates tournament took place in Moscow, Russia from 10 to 30 of March, 2016. The 2008 Corus chess tournament was a Grandmaster level chess tournament held in the de Moriaan Community Centre, Wijk aan Zee, Netherlands from 12 January to 28 January 2008.  It consisted of three main Grandmaster groups and the Honorary group, comprising former A group champions; groups A, B and C were won respectively by Levon Aronian (on tiebreak from Magnus Carlsen, after both finished with 8 points), Sergei Movsesian (9½ points, one point ahead of Nigel Short and Étienne Bacrot) and Fabiano Caruana (10 points, two ahead of Dimitri Reinderman and Parimarjan Negi).  The Honorary group was won by Ljubomir Ljubojević (4 points) ahead of Viktor Korchnoi, Jan Timman (both 3) and Lajos Portisch (2). The 1981 World Chess Championship was played between Anatoly Karpov and Viktor Korchnoi in Merano, Italy from October 1 to November 19, 1981.  Karpov won. The Chess World Cup 2013 was a 128-player single-elimination chess tournament, played between 11 August and 2 September 2013, in the hotel Scandic Tromsø in Tromsø, Norway.  It was won by Vladimir Kramnik, who defeated Dmitry Andreikin 2½–1½ in the final match.  The finalists qualified for the 2014 Candidates Tournament.
Answer: Robert Hübner