There are many ways to look at the idea of "Greatest Pro Wrestler of All Time" because there are many way that a person can achieve greatness. I looked at 3 main criteria: (1) there ability in the ring and/or on the mic, (2) there importance and impact on the history of professional wrestling, and (3) there impact on the fans - i.e. popularity, charisma, ability to make fans love/hate them.
http://www.ranker.com/list/greatest-pro-wrestlers-of-all-time/azzy_roth,
Ed Lewis
Frank Gotch
Gotch wrestled back when it was a legitimate sport and was World Heavyweight Champion from 1908 to 1913 - one of the ten longest in the history of wrestling. He was responsible for making the sport of wrestling popular and moving it from carnival side shows to major sports venues. His matches with George Hackenschmidt for the World Title are legendary.
George Wagner
Gorgeous George was the original flamboyant bleached blond. He was the model for both Nature Boys followed.
Hulk Hogan
Kurt Angle
Lou Thesz
Mildred Burke
If you don't know who she is, you should. She is the most impactful woman in wrestling history because she MADE women's wrestling. She started wrestling in circus side shows and had to overcome a bans on women's wrestling. Mildred Burke is the pioneer of today's diva's and knockouts. No women,even the Fabulous Moolah, would have a place in the professional wrestling ring if Burke never wrestled.
"Nature Boy" Buddy Rogers
The original "Nature Boy". Rogers over Flair because they would both agree that Rogers was the best Nature Boy.
Ric Flair
Classy Freddie Blassie