Khabib was one of the most dominant UFC fighters ever thanks in large to his ruthless wrestling base. He also won fans because of his noble persona and his loyalty to his family. The Dagestan native retired from the sport after he promised his mother that he would quit. Then he walked away in the prime of his career (via Mirror).
But Khabib also has a dark side because of his association with brutal dictators. He infamously met Vladimir Putin and Chechen warlord Ramzan Kadyrov multiple times. Furthermore, he spoke out against women competing in MMA. He is also infamously homophobic so he may not be the nice person that everybody thinks.