UFC lightweight champion Khabib Nurmagomedov said the best fighter in MMA history is Fedor Emelianenko. As for UFC, here, according to Khabib, the best is Georges St-Pierre.
"The number one in UFC is Georges St-Pierre, he is the champion in the cage and outside of it. Jon Jones is on the second place, Demetrious Johnson is on the third, he defended the title eleven times. But outside UFC and MMA in general Fedor Emelianenko is on the first place."