I'll get this out of the way up top... I know for some this will be a controversial topic given Tyson's well publicised troubles outside (and even inside) of the ring, however for the purposes of this post I'm only looking at Tyson the boxer.
For me, Mike Tyson aka Iron Mike is the greatest heavyweight boxer of all time.
Sometimes our view on stuff is clouded/tinted by the generation in which we grew up, and I was a teenager in 1980 so the early/mid 80s were deeply influential in my life. By the time of Tyson's first televised fight in Feb 1986 I was 18 and very impressed by what I saw, and the rest of my early adult life was dominated by Tyson's burgeoning career in the ring as opponent after opponent got obliterated by him.