From all the people who have been using TRT, I think Frank Mir was the most surprising. Guys like Marquardt, Hendo, Sonnen, and Rampage have cut a lot of weight which decreases testosterone levels over time. Belfort cuts a lot of weight too and in addition was using steroids (at one point in time).
Frank Mir cut weight twice in his career and before that in highschool (unsure how many times and how much weight). He's fairly young (33) too. I think cases like his is just abuse of PEDs (unless I am unaware of something), whereas someone like Hendo is credible.