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.
The poster for UFC 137: Penn vs. Diaz
Dennis D. Siver is a retired Russian-born German mixed martial artist who competed in the welterweight, lightweight, and featherweight division of the Ultimate Fighting Championship.
Dennis Siver