I wouldn't underestimate the popularity of some of the old greats in their time -- Morphy and Capablanca in particular.
But the answer has to be Kasparov -- the strongest player ever, and a dominant champion from the most chess-mad country on the planet, but also for his highly publicized matches against IBM's computers and outspoken political nature. Years after he's retired, he's probably STILL the most well-known chessplayer to most people.
Who is the most known chess player in history or the present. Is it Kasparov, Fischer, Capablanca, etc.? The first famous chess player i knew would have to be Fischer but thats just me and my first first, now i know almost all the famous players. BUT... which is the most widely known player now.