young Muhammad Ali / Cassius Clay: being light on your feet, speed over muscle, agility over power. Too much has been shown on his later career but it's really before he got the boot that's amazing. Watch his combo against Brian London and the full fight against Cleavland Williams. This is the shit that changed stand up.
Royce: for a lot of people he was the first to showcase bjj and changed the game
3rd place is either Fedor or Mike Tyson. In their primes they both influenced a lot of people.