UFC 100 was a mixed martial arts event held by the Ultimate Fighting Championship (UFC) on July 11, 2009 in Las Vegas, Nevada.

The event included two championship bouts (Heavyweight and Welterweight) and a fight between the two coaches of the most recent season of The Ultimate Fighter reality series on Spike TV. The main event featured a rematch between UFC Heavyweight Champion, Brock Lesnar, and UFC Interim-Heavyweight Champion, Frank Mir. This title unification bout occurred as a result of former UFC Heavyweight Champion, Randy Couture's year-long "resignation" from the company. During his absence, the UFC created an Interim-Heavyweight Championship that Antonio Rodrigo Nogueira had won by defeating Tim Sylvia. Nogueira and Mir were opposing coaches in The Ultimate Fighter: Team Nogueira vs Team Mir and would fight for the interim championship at UFC 92.

During the airing of the television program, Couture returned to the company and UFC President Dana White announced that he would defend his title against Lesnar at UFC 91. This meant that the winner of the Couture-Lesnar and Nogueira-Mir matches would face off for the undisputed crown. In his fourth professional fight, Lesnar defeated Couture via technical knockout to become the UFC Heavyweight Champion. Mir was crowned the interim champion after becoming the first fighter to ever finish Nogueira. The match between Lesnar and Mir was set for UFC 98. However, Mir suffered a knee injury during training and was forced out of the bout. It was announced a day later that the proposed fight would be moved to UFC 100 instead. Lesnar and Mir had fought once before, during Brock's UFC debut at UFC 81; which Mir won via a kneebar submission.

Brock Edward Lesnar (/ˈlɛznər/; born July 12, 1977) is an American professional wrestler, actor, former mixed martial artist and amateur wrestler, signed with WWE and appearing on its Raw brand. He is also a former UFC Heavyweight Champion and former #1 ranked mixed martial arts (MMA) Heavyweight by Sherdog; he was ranked #5 before he announced his retirement at the end of 2011. Lesnar is an accomplished amateur wrestler, winning the 2000 NCAA heavyweight wrestling championship and placing second in 1999, losing in the finals to 1999 world freestyle wrestling champion and future New England Patriots offensive lineman Stephen Neal.

He gained prominence in World Wrestling Entertainment (WWE) from 2002 to 2004, where he is a former three-time WWE Champion, becoming the youngest WWE Champion at age 25 with his first reign. Lesnar was the 2002 King of the Ring and the winner of the 2003 Royal Rumble. After leaving WWE, Lesnar pursued a career in the NFL. He played during the preseason for the Minnesota Vikings, but ended up being a late cut. Lesnar returned to professional wrestling at the end of 2005, and joined New Japan Pro Wrestling (NJPW), where he won the IWGP Heavyweight Championship in his first match. He was officially stripped of the title by NJPW in July 2006, and took the physical belt with him to Inoki Genome Federation (IGF), where he was still recognized as IWGP Champion until June 2007.

Dana White (born July 28, 1969) is the current President of the Ultimate Fighting Championship (UFC), a mixed martial arts organization based in the United States.

Born in Manchester, Connecticut on July 28, 1969, White grew up in Las Vegas, Nevada, Ware, Massachusetts and Levant, Maine. White is a passionate Boston Red Sox fan. During his youth, he bounced back and forth between Boston and Maine. He attended the University of Massachusetts Boston but did not finish; however, while there he did launch a boxing program for inner-city youth.

White has a background as an aerobics instructor. In 1992, White established Dana White Enterprises in Las Vegas. He conducted aerobics classes at three gyms in the Las Vegas area and began managing MMA fighters Tito Ortiz and Chuck Liddell.

While working as a manager, White learned that Semaphore Entertainment Group, the parent company of the UFC, was looking for a buyer for the UFC. White contacted childhood friend Lorenzo Fertitta, an executive at Station Casinos, and a former commissioner of the Nevada State Athletic Commission. Within a month, Lorenzo and his older brother Frank bought the UFC, with White installed as its president. White currently owns about 9% of Zuffa, LLC, the entity the Fertitta brothers created to own and manage the UFC.

Daniel Jeffery Henderson, (born August 24, 1970) is an American mixed martial artist and former Olympic wrestler, who competes as a middleweight and light heavyweight in the Ultimate Fighting Championship. He is the former Strikeforce Light Heavyweight Champion and was the last Welterweight 183 lb (83 kg; 13.1 st) and Middleweight 205 lb (93 kg; 14.6 st) champion of Pride Fighting Championships. He was the only mixed martial artist to concurrently hold two titles in two different weight classes in a major MMA promotion. Henderson is also the UFC 17 Middleweight Tournament Winner, the 1997 Brazil Open Lightweight Tournament Champion, the RINGS King of Kings 1999 Tournament Winner, and the 2005 PRIDE Welterweight Grand Prix Champion.

Henderson also owns the Clinch Gear MMA apparel brand. As of May 2012, Henderson is ranked the #2 light heavyweight by Sherdog.

Dan Henderson was born in Downey, California and grew up in Apple Valley, California. He attended Victor Valley High School in Victorville, California, and earned medals at the California State Wrestling Championships in 1987 and 1988. He was a member of the 1987 Victor Valley High School wrestling team state champions. Henderson went on to wrestle at both Cal State Fullerton and Arizona State University, participating in the 1993 NCAA championships. He represented the United States in the 1992 and 1996 Summer Olympics in Greco-Roman wrestling.

Michael Gavin Joseph Bisping (born 28 February 1979) is an English mixed martial artist. He fights in the middleweight division of the Ultimate Fighting Championship and is the former Cage Warriors Fighting Championship Light Heavyweight Champion, former Cage Rage Light Heavyweight Champion and The Ultimate Fighter 3 Light Heavyweight Tournament winner. As of March 2012, Bisping is ranked the No. 4 middleweight in the world by Sherdog.

Bisping was born in manchester UK in 1979, but moved to Bridlington, East Yorkshire, England when he was a child. Taking an early interest in martial arts, Bisping began training in a traditional form of jiu-jitsu known as Yawara Ryu under Paul Lloyd Davies when he was 8 years old. In 1994, at the age of 15, Bisping competed as an amateur in England's first "no holds barred" competition, a precursor to modern MMA, called Knock Down Sport Budo (KSBO), organised by Davies.

At the age of 18, Bisping decided to abandon his martial arts training in order "to pursue real life". But less than a year later Bisping began training kickboxing and karate on the advice of Alan Clarking, owner of Black Knights gym, who saw potential in the young fighter. Bisping enjoyed a short, but successful kickboxing career, winning the North West Area title and later the Pro British light heavyweight kickboxing title. After again briefly quitting competition in 1998, Bisping returned to kickboxing to take the Pro British light heavyweight title for a second time. Soon after winning his second kickboxing title, Bisping was forced to abandon his full-time training for a "real job". Bisping worked in factories, slaughterhouses, as an upholsterer, a postman, a tiler, a plasterer, a double-glazing door salesman,production line operative making barbecues at Rectella in Clitheroe and also a relatively successful DJ around the north-west club scene.