Chess grandmaster Victor Korchnoi, a prominent Soviet defector who saw his citizenship restored by Mikhail Gorbachev in the waning days of the USSR, has died. He was 85.

The Russian chess federation says Korchnoi died in Switzerland, where he had lived for decades.

Korchnoi was one of the leading Soviet chess players before defecting in 1976 in the Netherlands. His matches against the official Soviet champion, Anatoly Karpov, became famous as duels on political, psychological and physical levels.

Korchnoi tried and failed twice to unseat Karpov as world champion.

In August 1990, Korchnoi welcomed as an "important step" Gorbachev's move to restore his Soviet citizenship, along with 22 others including novelist Alexander Solzhenitsyn. But Korchnoi said it wasn't enough to make him return to the Soviet Union.