#1. Goldberg - Usually refuses to turn heel in WWE
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Many WWE fans love trashing Goldberg, but they can't deny the true drawing power he has. Goldberg is one of the few characters in WWE that has a "larger than life" feeling, and it's not surprising that Vince McMahon keeps breaking out his checkbook for him to wrestle for a few minutes.
Goldberg has gotten booed several times from WWE fans, and a heel run would make a lot of sense if he keeps returning annually the way he does. When asked about a heel turn, Goldberg has always shut down the idea - stating that he wants his persona to be like a superhero to kids.
He's well past his prime, and since he occasionally returns, a heel turn for him would be massive. We've never seen a heel Goldberg in WWE, and if he turns, it could result in his best run to date.
One thing is for sure - WWE fans will be far more excited to see a heel Goldberg than a babyface one.