Former world chess champion Garry Kasparov has come out of professional retirement for a one-off tournament in St Louis, Missouri.
The 54-year-old from Azerbaijan has been out of the game for 12 years, after turning his hand to politics.
He gained legendary status, becoming known as the "Beast of Baku" and dominated the sport for 15 years.
In a Facebook post he said: "This is not an end to my retirement from chess, only a five-day hiatus."
He added that any earnings from the competition will be donated to charity.
Mr Kasparov was selected as a wild card to compete in the Rapid and Blitz tournament against nine of the best players in the world.
The competition's format requires players to make moves much faster than in the ordinary game.
However, the current world champion, Norwegian Magnus Carlsen, is not there.
In 1985 Mr Kasparov became the youngest-ever world champion, maintaining the title for 15 years.
He was a pioneer of using technology in the game, but was famously beaten by an IBM super computer Deep Blue in 1997.
Mr Kasparov stepped away from the sport in 2005, becoming a vocal opponent of Russian President Vladimir Putin.
He has taken part in significant demonstrations against the Russian leader and set up the Other Russia opposition group.
In 2013 he left Russia and moved to New York.