Connie Hawkins is arguably the first player we’d recognize as modern but the player most people would identify as changing the game to what we now expect was Julius Erving, aka Dr. J.
He said that when he got to the ABA and could run and dunk he felt freed. He first redefined the ABA and then after the merger the NBA.
Some of the clips here are very early. In particular look at the one scene from a park - you’ll notice dozens and dozens of fans sitting along the top of a roof to watch.