Garry Kasparov

World chess champion from 1985 to 2000 and, at 22, the youngest ever to hold the undisputed title, Kasparov spent a record 255 months ranked world No. 1. His 1997 loss to IBM's Deep Blue was the first time a reigning champion was beaten by a computer under standard time controls, a result that reshaped public understanding of what machines could do far beyond chess. Since retiring from competition in 2005, he has written on strategy and become an outspoken critic of Vladimir Putin, campaigning from exile for democratic reform in Russia.