Hatsu Hioki is a Japanese professional mixed martial artist competing in the featherweight division. He is the former Shooto Lightweight Champion, Sengoku Featherweight Champion, and TKO Featherweight Champion. Hioki is a long time Shooto veteran and has fought most of his fights in Japanese promotions including the largest mixed martial arts organization at the time, Pride Fighting Championships.

UFC 137: Penn vs. Diaz was a mixed martial arts (MMA) pay-per-view event held by the Ultimate Fighting Championship on October 29, 2011, at Mandalay Bay Events Center in Las Vegas, Nevada.