Wilhelm Steinitz. Credit: 'Wilhelm Steinitz' entry in www.wikipedia.com .
There is an old story -- or, rather, libel -- that Steinitz (incidentally, a Jew, of course) had once said that he could beat God even if he gave God pawn-and-move odds. Naturally, no exact source is ever given for this alleged saying, and it is merely repeated from one book to another whenever an incident about the alleged insanity of chess players in general, and masters in particular, is needed to spice up the book.
In Alifut Yisrael be'Shachmat 1961/62 ('Israeli Chess Championship 1961/62', Ed. Eliahu Shahaf, "Mofet" press, Tel Aviv, 1962), we find, however, a different version of the story (p. 19):
Wilhelm Steinitz, who was self-confident enough to once say that even God couldn't give him pawn and move... Naturally this version of the story is unattributed, and it is used to "spice up" an article about opening theory. However, it follows Irving Chernev's The Bright Side of Chess  in suggesting that Steinitz did not claim he could beat God while giving pawn-and-move odds, but merely that God could not beat him if God gave him pawn-and-move odds. (See Edward Winter's article, Steinitz versus God).
There is, naturally, a great difference between the two claims. In Chernev's and Shahaf's version of Steinitz's quip, 'God' is just a metaphor for 'a perfect player', and the claim is pure Steinitz: colorfully put and not suffering from false modesty, but in essence simply the insightful (and perhaps true) claim that the playing strength of the best masters of his time had so improved, that it practically close to perfection. (This happened, presumably, due to the new, scientific understanding of the game's strategy, of which Steinitz was the most important developer.)
One wonders (see also Winter's article) whether Steinitz really made either claim. It is doubtful he ever did. But, if he did, I would bet a significant sum he made the latter claim, and that sensation-seeking writers, making use of Steinitz's real mental illness at the end of his life as an excuse to print "crazy chess player" canards, turned the story on its head and made Steinitz's perfectly reasonable remark into "proof" of megalomania.