Mike Tyson, certainly up until Buster Douglas at least, built up an 'aura of invincibility'. People thought he could not loose and fighters were mentally shot before they got in the ring. Which other fighters have manged to build something similar?
GGG managed it in a different approach to Mike, he wasn't intimidating at all but his reputation was rock solid probably right up until he fought Jacobs. Kovalev certainly had an edge to him with his 'Krusher' brand, post Andre Ward he has been a shadow of his former self.
If all was fair GGG would still be the undefeated Middleweight Champion of the World. In my opinion he still is Canelo has NEVER LEGITIMATELY beaten him & cannot
Fury definitely has it, people seem to think there is no way to beat him, If you run he runs better if you bang he will Kronk you. Joshua was on a good run in the publics eye until the Takam fight. People believed he could just bulldoze any opponent. Disagree. Loma is great to watch technically but he is vulnerable, partially because he is fighting above weight also some of his fights have been close calls.
It's impossible to convey the surprise - shock even - of 'Iron' Mike Tyson going down heavily then on all fours groggily putting his gum shield back in sideways in 1990. Damn...
Hagler from my generation ... always showed up in shape and ready for war; you'd be hard pressed to find anyone more consistently dedicated for such a long career (67 bouts; 62 wins, 3 losses, two draws)
George foremann before the muhammad ali fights a good shout. Started looking a bit unbeatable after norton and frazier demolitions.
Foreman pre 74. Carlos Monzon. Roman Gonzalez pre Srisaket. Hagler. All I can think of off the top of my head.