As a guitarist I have to mention BB King. Literally every guitar player since the 50’s has been influenced by him in some way. Even John said in multiple interviews how much he was influenced by him. And he’s not even remotely what you would call a blues purist like Clapton.

Him or Muddy Waters for blues roots.

Jimi Hendrix has to be the most single influential artist if we’re talking about rock. I think it’s safe to say the guitar may not even have thrived as it has as an instrument without his influence. He is the transition between 50’s clean rock and metal. At least the main transition.

I see a lot of Micheal Jackson. I agree that he’s up there, but I think he was more famous as an overall package, dancer, and performer than for his musical ability. I love me some billie jean, but he never did anything to really revolutionize music. He was more of a pop icon.