#1 “Stone Cold” Steve Austin
WWE Hall Of Famer Stone Cold Steve Austin was once a top superstar of the Attitude Era during the rise of the WWF. He did play a huge role in that time to help the company win the Monday Night Wars against WCW. He was one of the best attractions in the world of professional wrestling, and if Reigns would have feuded with him, then it could have changed his career in one go.
Stone Cold was once a perfect heel of the WWF and later became one of the best babyfaces of that era. However many would say that he was more like an anti-hero, but overall he could have helped Reigns in any way.
As of now, WWE sees him as the new face of the company so it is likely that the Big Dog would have had a face vs heel feud with Austin. If we talk about the heel Austin, then it could have been a career-changing match for Reigns as the fans loved to boo the latter that time. It could have helped Reigns to establish himself as the top guy.