Paul Keres

Many chess historians consider Keres one of the greatest players in history, and the strongest player never to become world champion.

Paul Keres was one of the very few players who had a plus record against Capablanca. He also had plus records against World Champions Euwe and Tal, and equal records against Smyslov, Petrosian and Karpov. He beat every world champion from Capablanca through Bobby Fischer (his two games with Karpov were drawn), making him the only player ever to beat nine undisputed world champions.

"Keres is one of the nicest people that I have ever had the pleasure of meeting. With his friendly and sincere smile, he makes friends easily. He is goodnatured and kind. Yes, he loves chess, but being a human being is his first consideration. In addition to chess, Keres was interested in tennis, Ping-Pong, swimming, and bridge" (Samuel Reshevsky).

http://www.chessgames.com/perl/chessplayer?pid=21922