Demetrious Johnson is a former American mixed martial artist. He began his career in World Extreme Cagefighting and shifted to the Ultimate Fighting Championship roster when those companies merged in 2010. In 2012, he became the inaugural UFC Flyweight Champion, defending his title numerous times. In 2018, Johnson was traded to ONE Championship, and he became ONE Flyweight Champion the following March. He is widely regarded as one of the greatest MMA fighters of all time.