Rudy is much more than simply 9/11, although that terrible day and the way in which he handled it is nothing short of admirable, and it became his defining moment for many skeptics.
But Rudy became St. Rudy way before that day, when he first started to become a force in NYC politics during the mid 80's. Combatting organized crime as US Prosecutor, running (and losing, closely) his first run for Mayor in '89 vs. the inept Dinkins, and then finally winning in '93 ... the skeptics all predicted that he'd fall flat on his face trying to govern an 'ungovernable city'.
Rudy showed 'em all, and turned the city completely around. Street crime dropped dramatically, the municipal unions were forced to surrender some of their stranglehold on city finances, Times Square became an oasis of investment and tourism instead of the blight of peep-shows and urban decay that it had become before.
NYC under Rudy's watch became the template for the revitalization of cities all over the country. It wasn't just about 9/11
that's OK, you've got to play the hand you are dealt.