#2 Brock Lesnar
Despite a less than spectacular start to his MMA career, Brock Lesnar soon established himself as a dominant force in UFC’s Heavyweight division, registering impressive victories against the likes of Randy Couture, Shane Carwin, and Frank Mir on his path to the UFC Heavyweight Championship.
Then came the fateful fight against Cain Velasquez. Getting mauled by Velasquez seemed to shake a deep-seated belief inside Lesnar and he never looked the same after this TKO loss. He would make one more appearance as an MMA fighter before quitting the business for half a decade.
Another early loss to Alistair Overeem back in 2011 caused Lesnar to pack his bags and head back to pro-wrestling till he made his return to the octagon in 2016 against Mark Hunt. An initially triumphant return was soured as The Beast tested positive for PEDs and his victory was overruled to a No Contest.
Lesnar recently announced his retirement from the UFC.
