Glad to see Charlie and Dragon Promotions finally getting their due respect here on AZ, But determining the most positive influence on pool of all time is a title even Charlie can't handle (and I am a fan of the man).
My vote would be for the unknown soul that invented 9 Ball (the 1920's perhaps?) That mysterious gentleman took a slow moving game and changed it into something quick, easy to understand, and TV ready for mass public consumption. He laid the groundwork for all of the movies and television tournaments that followed and allowed the sport to grow into what it is today (okay, it's not exactly the PGA, but you get my point).
I would loved to have seen it, some guy in a pool room with gas-powered lights getting waxed in straight pool time after time, loosing money to paperboys and card sharks until he has had enough. So he gets inventive and comes up with a new game, one that gives him a gambler's chance at winning once in a while. "Hey Pops," he might have said. "What's about we play again, and this time, yuz got to sink em' in order. Yeah, that's right. And none of em' matter cept' the nine ball. That's the cheese ball Pops, nothing else."
And the game was on.
Now if we could just get rid of it ... sigh.