The game’s mental and physical toll eventually forces most top players to stop competing. And those who continue to play tend to avoid the elite tournaments where the pressure is greatest.

Then there is Viktor Korchnoi.

He was a top player for more than 30 years and competed for the world title three times. The last of those battles was in 1981, when he was 50. Four years ago, when he was 75, he was still ranked No. 85 in the world.

Korchnoi will be 80 in March, and his ranking has slipped to No. 460. But he can still be a formidable opponent, and he has lost little of his zest for competition. (He earned the nickname Viktor the Terrible partly because of the way he reacted when he lost.)

He is currently entered in the Tradewise Gibraltar Chess Festival. The tournament, in Gibraltar, has become a magnet for top players, and Korchnoi was seeded 38th.