UFC 109: Relentless was a mixed martial arts event held by the Ultimate Fighting Championship (UFC) on February 6, 2010 at the Mandalay Bay Events Center in Las Vegas, Nevada.

A previously rumoured bout between Renzo Gracie and Matt Hughes did not take place on this card, but took place at UFC 112.

A Middleweight Championship bout between Anderson Silva and Vitor Belfort was confirmed by UFC President Dana White, although it was contingent on Silva's successful recovery from elbow surgery. Subsequently, the fight was rescheduled due to Silva's continued slow healing from surgery. The Silva vs. Belfort bout was expected to take place at UFC 112, however Belfort was forced to withdraw from the fight & Demian Maia replaced him, after number 1 contender Chael Sonnen was not clear to fight.

Antônio Rogério Nogueira had to withdraw from his bout against Brandon Vera due to an ankle injury. It was announced that Vera will face Jon Jones on March 21, 2010 at UFC Live: Vera vs. Jones.

Josh Koscheck was scheduled to face Paulo Thiago, but was forced off the card with an injury. Mike Swick stepped in as Koscheck's replacement and fought Thiago.

Chael Patrick Sonnen (pronounced /ˈtʃeɪl ˈsʌnən/; born April 3, 1977) is an American mixed martial artist who competes as a middleweight in the Ultimate Fighting Championship. He was an NCAA Division I All-American wrestler at the University of Oregon, a silver medalist at the 2000 Greco-Roman World University Championships, as well as a two-time Dave Schultz Memorial International Greco-Roman winner.

As of October 2011^[update], Sonnen is ranked as the No. 2 middleweight in the world by Sherdog.

Sonnen was born Chael Patrick Sonnen on April 3, 1977 in West Linn, Oregon.

Sonnen started his MMA career at the age of 19 in 1997 by defeating Ben Hailey in Vancouver, Washington. His second fight was against future ICON Sport Middleweight Champion and Strikeforce Middleweight contender Jason "Mayhem" Miller. Sonnen went 6–0 in his first six fights, until his loss to Trevor Prangley, which he later avenged in 2006 at UFC Ultimate Fight Night 4. He also fought The Ultimate Fighter winner and former UFC Light Heavyweight Champion Forrest Griffin.

Matthew John Serra (born June 2, 1974) is an American mixed martial artist and Brazilian Jiu-Jitsu black belt. He is a former UFC Welterweight Champion and an ADCC Submission Wrestling World Championship silver medalist. He began practicing martial arts at an early age, first studying kung fu. In the 1990s, he began studying Brazilian Jiu-Jitsu under Renzo Gracie and on May 23, 2000 he obtained his black belt, the first American to do so under Gracie. He is one of only two people in MMA to defeat Georges St-Pierre, the other being UFC Hall of Famer Matt Hughes.

Serra won first place at the Brazilian Jiu-Jitsu Pan American games in 1999 and won third place at the 1999 World Championships in Brazil as a brown belt. Continuing his Martial Arts career, he competed in the ADCC Submission Wrestling World Championship choking out Takanori Gomi, winning a decision over Jean-Jacques Machado, and placing 2nd in the 66–76 kg division. Serra was invited to compete in Pride 9 against Johil de Oliveira but the bout was called off at the last minute when Oliveira was burned in a pyrotechnics accident backstage. Soon after, Matt began to compete in the UFC organization where he built up a record of four wins and four losses. One of the losses was a close decision fight with future Welter and Lightweight champ B.J. Penn which would have earned him a title shot in the failed Lightweight tournament.

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.

Randy Duane Couture (pronounced /koʊˈtʊər/; born June 22, 1963) is an actor, retired American mixed martial artist, collegiate and Greco-Roman wrestler. During his tenures in the Ultimate Fighting Championship (UFC), Couture became a three-time UFC Heavyweight Champion, two-time UFC Light Heavyweight Champion, an Interim UFC Light Heavyweight Champion, and was the UFC 13 Heavyweight Tournament Winner. Couture is the first fighter to hold two UFC championship titles in two different divisions (heavyweight and light heavyweight). Couture has competed in a record 15 title fights. He holds the most title reigns in the UFC with five. His last fight with Lyoto Machida marked his 24th fight in the UFC, the third most amount of fights in the UFC (Tito Ortiz is first with 26 and Matt Hughes is second with 25). Couture is one of the first members of the UFC Hall of Fame. He is the only person over the age of 40 to have won a UFC championship fight, having done so four times.^{[citation needed]}

Couture was an Olympic wrestling alternate and has lived in Corvallis, Oregon, throughout much of his career, where he served as an assistant wrestling coach and a strength and conditioning coach for Oregon State University. He established Team Quest with Matt Lindland and Dan Henderson, a training camp for fighters, based out of Gresham, Oregon, and headed by coach Robert Folis. In 2005, Couture moved to Las Vegas, where he opened his own extensive chain of gyms under the name Xtreme Couture. He currently trains at his Las Vegas-based gym. Couture partnered with Bas Rutten in the opening of Legends Gym in Hollywood, California.