Bob Hayes changed the Cowboys from bad to very good. His raw speed made the Cowboys offense the most dangerous in the NFL. Defenses were so busy trying to defend his speed that they developed the first deep zones which allowed the Cowboys to become a dominate running team. The Cowboys never had a winning season until Bullet Bob arrived and from his rookie year in when '65 when they finally had a non losing season (7 wins & 7 losses) they would have 20 consecutive winning seasons. I think Tony Dorsett, Everson Walls, and Micah Parson all are good answers but, in my mind Bob Hayes literally changed how the game was played. In years to come, we might look back and say that Micah changed the game with his versatility but, today I would say Bob Hayes is still the man.