If we break this down to standard wrestling matches, Sammartino, Andre, Austin, Lesnar, Flair, Hogan, Warrior and maybe Triple H are seemingly the ones that usually come out on top more than the others. Maybe Cena now but I don't watch wrestling anymore. At some point in time, each of them has been the most dominant wrestler in existence. Before Hogan, Andre may have been the most popular ever. Before him, it was probably Lou Thesz who was the main star on nationally televised wrestling in the 1950s.
Of course, it's not just a matter of how invincible someone was presented to be but for how long. Sammartino was invincible for eight years, the longest anyone was ever the WWE (WWWF) Champion and undefeated. On the other hand, nobody in that era was presented as being as superhuman as the Undertaker or Lesnar. Based on long term success, I'd give it to Sammartino but Hogan may still be the most popular ever which tends to mean wins and if it were for real, Thesz, who isn't even in the competition, would beat any of them except maybe Lesnar or Angle.