In his time Foreman was considered the most intimidating (Liston 2.0) because of the way he tore through the 200 lbs Americans who beat Ali and he did it in a couple of rounds, clubbing them to the ground relentlessly before it was waved off. Prime Tyson intimidated many of his opponents but there were a number of big journeymen and fringe contenders who weren't scared of him and they generally went the distance or even beat him. At least "big George" was big for his time: 5'10 Tyson was too small to scare many decent 6'3+ heavies. KO artists are intimidating because they often switch the lights off with one punch, the best of them like Wlad or Wilder can do it both early and late. Vitali was intimidating in a different way because he was more likely to give his opponents a severe and sustained beating and their puncher's chance was either small or almost non-existent. Along with power which is the most visceral, the overall quality of the opponent makes him intimidating, particularly if he is likely to beat you in a humiliating fashion.
Sonny Liston was the original bad man…. He was a real thug and leg breaker and was a menacing figure. Tyson and Foreman come after Sonny IMO.
Reputation Tyson in his prime. Lewis ducked his fair share too - Bowe avoided him like the plague whilst King put off from making the Hollfield and Tyson fights for as long as he could. However if we going on most reported ducked HW ever then I can't anyone being reportedly duckes more than AJ.
I'd put David Tua in there. After watching his 19 second ko of John Ruiz, I always think, this is what a 219 lb man looks like when you put him through a blender. But from the stories on Youtube, even more intimidating would be Haku/Meng of WWE fame.
Remember the stare down Iron Mike with McNeely during ref instructions, props to McNeely for not peeing in his pants. Or maybe he did.
Even when I watch Tyson in interviews today, I worry someone is gonna say the wrong thing and get a tight hook uppercut combo.... I'm sitting at home physically worried for these guys that are in the same room as him.
George Foreman in his prime had a pretty formidable presence. Same for that young, fresh, Mike Tyson. They had an aura, and fighters felt like they were risking their personal safety going anywhere near them.