Some of his work, via Flikr.
If you live in NYC and ride the subway, you may have seen some of these:
PosterboyNYC
"Impossible is just a big word thrown around by small men who find it easier to live in the world they've been given than to explore the power they have to change it. Impossible is not a fact. It's an opinion. Impossible is not a declaration. It's a dare. Impossible is potential. Impossible is temporary. Impossible is nothing.”
~ Muhammad Ali