Tim Sylvia: The Maine-Iac has in fact tested positive for steroids in the past. Back when he first came into the UFC. His third fight in the Zuffa Organization actually.
It was after defeating Ricco Rodriguez for the belt. He was defending his belt against Gan McGee and won in devastating fashion.
After the fight, he tested positive for steroids and was not only stripped of the belt and fined, but suspended as well.
Tim has gone on the record as saying "it was for shedding excess body fat." That may be true, but if that's the case, get a better trainer or a fitness trainer to help you do it.
Royce Gracie: The Original UFC Champion. The man who brought Brazilian Jiu Jitsu to the rest of the world.
Yes, he has in fact tested positive for steroids. It was after he avenged his loss to Kazushi Sakuraba in 2007.
I doubt the possibility that he did steroids because if you look at the guy, he just doesn't look like he's used them before.
Maybe he was healing an injury. But he did test positive, so you never know who is using.
Brock Lesnar: Lesnar has consistently denied ever using steroids. He's never tested positive, but anyone with a brain can clearly see that when he wrestled in the WWE, he was a juice head.
He's the same exact weight as he was back then, but look at the difference in his physique. He's not on them now, but he definitely used steroids or other performance enhancing drugs back in the day.