Nate Diaz MMA. Nathan Donald Diaz (born April 16, 1985), professionally known as Nate Diaz, is an American mixed martial artist currently competing for the UFC in the Lightweight division and won The Ultimate Fighter 5. He is the younger brother of mixed martial artist Nick Diaz. In addition to the UFC, Diaz has competed in the WEC, Strikeforce, and Pancrase in Japan.