Jim Kelly - obviously Marv Levy deserves some credit for implementing the strategy, but Kelly was the first QB to use a no huddle at the start of the game and throughout it while calling the plays at the line of scrimmage. Peyton Manning may have perfected it.
edit for spelling
Kelly didn't "change the NFL" though. Let's put aside the fact that he's not the person who invented (or even popularized) the No Huddle (as well as the fact that pretty much every team in the league ran the no huddle at some point or another even back before he entered the league). You're claiming he "changed the NFL" by introducing the No Huddle as an every down offensive attack. Which explains why there are approximately 0 teams today that run the No Huddle as an every down offensive attack.Being the first to do something doesn't mean you "changed the league". Warren Moon didn't "change the league" by running the Run-n-Shoot. Steve Spurrier didn't "change the league" by running the Fun-n-Gun. You could argue that Ronnie Brown did far more to "change the league" than Jim Kelly, because there's a much greater difference between the number of teams running the Wildcat before Ronnie and after Ronnie than there is difference between teams running the no huddle before Kelly and after Kelly.
Besides, the thread is about players who changed the league, and Jim Kelly doesn't get credit for his coaches' scheme, any more than Ken Anderson or Joe Montana get credit for "inventing" the West Coast Offense (that was all Walsh, baby, even though Anderson was the first and Montana was the best). Just like Tom Nalen doesn't get credit for the changes to the league as a result of Alex Gibbs' blocking scheme, and like no Pittsburgh LB gets credit for the changes to the league as a result of Lebeau's zone blitz.