Sean Keith Sherk (born August 5, 1973) is a retired American mixed martial artist and former UFC Lightweight Champion.
 Sherk competed in the Ultimate Fighting Championship and was one of the first combatants to have been a championship competitor in multiple weight divisions (having also competed for the UFC Welterweight Championship).
 He was the second UFC Lightweight Champion in the organization's history after Jens Pulver vacated his title 5 years earlier.
 Sherk also spent time competing in the Japan-based organizations, PRIDE Fighting Championships and Pancrase; going undefeated in both promotions.
 He holds one of the longest undefeated streaks in mixed martial arts history, with only four career losses, all to fellow-UFC Champions.
 Sherk announced his official retirement from mixed martial arts competition in September 2013 having last fought three years prior.
Joseph Edward Lauzon Jr. (born May 22, 1984) is an American mixed martial artist competing in the UFC's Lightweight division.
 He is tied with Nate Diaz as having the most post-fight bonus awards in UFC history.
 Joe's younger brother, Dan Lauzon, is also a mixed martial artist.
Frank Shamrock (born Frank Alisio Juarez, III; December 8, 1972) is an American former mixed martial artist.
 Shamrock was the first to hold the UFC Middleweight Championship (later renamed the UFC Light Heavyweight Championship) and retired as the four-time defending undefeated champion.
 Shamrock was the No. 1 ranked pound for pound UFC fighter in the world during his reign as the UFC Middleweight Champion.
 Shamrock has won numerous titles in other martial arts organizations, including the interim King of Pancrase title, the WEC Light Heavyweight Championship and the Strikeforce Middleweight Championship.
Rashid Magomedgadzhievich Magomedov (Russian: Рашид Магомедгаджиевич Магомедов ; born May 14, 1984 in Dagestan) is a Russian mixed martial artist of Dargin heritage, he is a former amateur Light heavyweight (179 lbs), Middleweight (165 lbs) boxer and current lightweight mixed martial artist competing in the Ultimate Fighting Championship.
 Magomedov is also a former M-1 Global welterweight champion.
 He is currently the #15 ranked lightweight in UFC rankings as of 5 November, 2016 and 20 April, 2017.
Luke Skyler Rockhold (born October 17, 1984) is an American mixed martial artist competing in the UFC, where he is the former UFC Middleweight Champion.
 He won the title on December 12, 2015 by defeating prior champion, the undefeated Chris Weidman via 4th round TKO.
 He lost his belt in his first title defense against Michael Bisping, who stepped in after Weidman pulled out of their scheduled rematch.
 A two-time world champion, Rockhold also won the Strikeforce Middleweight Championship by defeating Ronaldo Souza on September 10, 2011 via unanimous decision.
 Rockhold defended the title twice and was the last man to hold the belt, before Strikeforce was officially taken over by the UFC.
 He is currently ranked the #2 middleweight and #12 official pound-for-pound fighter by the UFC and other publications like Fight Matrix and Sherdog.
 Luke is also an avid surfer and skateboarder.
Alexis Davis (born October 4, 1984) is a Canadian mixed martial artist competing in the Ultimate Fighting Championship (UFC).
 She is a black belt in both Japanese Jujutsu and Brazilian Jiu-Jitsu.
 She is also a Canadian Open grappling champion.
 Davis at one point was the #9-ranked pound-for-pound female mixed martial arts (MMA) fighter in the world by MMARising.com and the #5-ranked 135-pound female fighter according to the Unified Women's MMA Rankings.
 In April 2015, she was the #3 ranked woman in the official UFC women's bantamweight rankings.
Christopher James "Chris" Weidman (born June 17, 1984) is an American mixed martial artist.
 He is the former UFC Middleweight Champion.
 He is currently ranked as the #6 middleweight in the world.
 In 2013, he earned worldwide prominence by becoming the first man to defeat Anderson Silva inside the UFC to become the Middleweight Champion, which he held for approximately two and a half years.
 Chris Weidman successfully defended the belt three times before losing it to Luke Rockhold.
Stephen Randall Thompson (born February 11, 1983) is an American professional mixed martial artist and former professional full-contact kickboxer who currently fights as a welterweight in the Ultimate Fighting Championship.
 Thompson is undefeated through 37 amateur and 57 professional kickboxing matches, with 40 wins by knockout.
 He is currently #1 in official UFC welterweight rankings and ranked as the #2 welterweight in the world by Sherdog.
 He has trained with former UFC Welterweight Champion Georges St-Pierre and currently trains with his brother in law, former UFC Middleweight Champion Chris Weidman.
Daniel Jeffery Henderson (born August 24, 1970) is an American former mixed martial artist and Olympic wrestler, who last competed as a middleweight in the Ultimate Fighting Championship.
 He was the last Strikeforce Light Heavyweight Champion and was the last Welterweight (80 kg ) and Middleweight (95 kg ) champion of Pride Fighting Championships.
 Additionally, Henderson was the Brazil Open '97 Tournament Champion, the UFC 17 Middleweight Tournament Champion, the Rings: King of Kings 1999 Tournament Champion and the Pride Weltwerweight Grand Prix Tournament Champion.
 During his career, Henderson also challenged for the UFC Middleweight Championship (2x), the UFC Light Heavyweight Championship and the Strikeforce Middleweight Championship.
 He was the first mixed martial artist to concurrently hold two titles in two different weight classes in a major MMA promotion.
 At the time of his retirement after UFC 204, he was the oldest fighter on the UFC roster.
 Known to be one of the greatest mixed martial artists of all time having defeated a total of seventeen MMA world champions across four major MMA promotions (UFC, PRIDE FC, Strikeforce, and RINGS).
Chris "The Westside Strangler" Brennan (born October 12, 1971) is an American mixed martial artist who competes in the Lightweight division.
 He has competed for the UFC, PRIDE, King of the Cage and Shooto.
 He is a former King of the Cage Middleweight Champion and former King of the Cage Middleweight Superfight Champion.
 He is also one of 18 fighters to compete in the -77 kg division at the ADCC Submission Wrestling World Championships in 2005.
 Chris was also the founder of Nogi Industries, a Mixed martial arts clothing company.
 In 2014 Chris was inducted in to the Mixed Martial Arts Hall of Fame.

Question: What is the name of the American mixed martial artist competing in the UFC, born in 1984, and winning the Middleweight Championship against Chris Weidman?
Answer: Luke Rockhold