"The guy who is my hero, and who I think is the greatest wrestler of all time, that’s Ric Flair. So I do appreciate the comment but I have a different opinion about who is the best wrestler and the greatest of all time, I have to go with Flair. It’s in his blood he laid the groundwork. He raised the bar that no one has really been able to follow as far as work ethic.” - Hulk Hogan
Sean Michels, Stone Cold, Hulk Hogan, Undertaker, HHH, Dusty Rhodes, all called Flair the greatest wrestler of all time. IMO, #1 isn't close. Hogan said something like 'Flair wrestled 60 minutes several times a week, I never even did it once.'
If you're talking about in-ring only, it's an entirely different list. Then you're bringing in amazing wrestlers like Ricky Steamboat, Chris Benoit, etc. Flair is probably the only one who could make the list based on his work, and based on his promos.
First out: Dusty Rhodes. Northerners who didn't watch southern wrestling would have no idea how big Rhodes was. He was the Crocket/WCW counter to Flair's heel for much of the 80s.
It's probably unfair to not include Andre, but the Andre I saw was so overweight and crippled he could barely move. Worldwide, he was probably unrivaled in popularity.