#3 Gegard Mousasi
Gegard Mousasi has fought in several highly reputable Mixed Martial Arts promotions all over the world and has achieved tremendous success everywhere he competed. Mousasi was in line for a shot at the UFC Middleweight Title, however, he couldn't come to terms with the new deal being offered to him by the company.
Resultantly, Mousasi entertained offers from other companies and ended up signing with Bellator MMA. 'The Moose' eventually captured the Bellator Middleweight Championship, and successfully defended the title in a 'Champion vs. Champion' super-fight against reigning Bellator Welterweight Champion Rory Macdonald.
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Mousasi dominated Macdonald on the feet and proceeded to also out-grapple the latter, beating Macdonald via TKO. Mousasi is beyond the shadow of a doubt one of the greatest Mixed Martial Arts fighters of all time, and most combat sports pundits believe that had he stuck around with the UFC, he'd probably have beaten Robert Whittaker for the UFC Middleweight Title.