Question: What was the nickname of the reigning, retired heavyweight champion at the time of the Fitzsimmons vs. Sharkey Heavyweight Championship boxing match?

Context paragraphs:
UCW-Zero Heavyweight Championship: The UCW-Zero Heavyweight Championship is the primary singles championship title in Ultra Championship Wrestling-Zero.  It was first won by Blitz Mason in March 2003 and defended throughout the state of Utah, most often Salt Lake City, Utah, but also in the Rocky Mountains and the Southwest United States.  The title was formerly recognized by AWA Superstars from 2005 to 2007, and then by the National Wrestling Alliance when the promotion became an NWA territory that same year.  On February 26, 2011, the UCW-Zero Heavyweight Championship was around the waist of Los Mochis Paco until it was stolen by Tyler Cintron after Junior X attacked Paco.  Later, Paco retrieved his belt back from Tyler Cintron.  The following show however, Tyler Cintron walks into the ring with his own UCW-Zero Heavyweight Championship.  UCW Director Blitz decide to make a Triple Threat TLC Match to determine the Undisputed UCW-Zero Heavyweight Champion which took place on June 4, 2011.  Los Mochis Paco was the victor to become the Undisputed Heavyweight Champion.  It would however be short lived because Los Mochis Paco was attacked by Black Out in the back and broke his leg and was unable to defend it.  Two Weeks later on June 18, 2011, Director for the night and Former 4 time UCW-Zero Heavyweight Champion Martin Casaus made a Gauntlet Match to determine a New Champion.  In the end, it was Junior X that prevailed and became the NEW UCW-Zero Heavyweight Champion.  2011 Rocky Mountain Rumble Champion Kid Kade went on to win the UCW-Zero Heavyweight Champion after defeating Junior X at "Meltdown Mayhem" on August 13, 2011.

Lennox Lewis vs. Mike Tyson: Lennox Lewis vs. Mike Tyson, billed as "Lewis–Tyson: Is On", was a professional boxing match that took place on June 8, 2002 at the Pyramid Arena in Memphis, Tennessee, United States, between IBF, IBO and WBC heavyweight champion Lennox Lewis and former IBF, WBA and WBC heavyweight champion Mike Tyson.  The fight was for Lewis' heavyweight championship titles.  Lewis defeated Tyson by knockout in the eighth round.

Fitzsimmons vs. Sharkey: The Fitzsimmons vs Sharkey Heavyweight Championship boxing match between Bob Fitzsimmons and Tom Sharkey was awarded by referee Wyatt Earp to Sharkey after Fitzsimmons knocked Sharkey to the mat.  Earp ruled that Fitzsimmons had hit Sharkey when he was down, but very few witnessed the purported foul.  The fans at the December 2, 1896 fight in San Francisco booed Earp's decision.  It was the first heavyweight championship fight since James J. Corbett, the prior champion, had retired from boxing the year before.  The fight may have been the most anticipated fight on American soil that year.

World Heavyweight Championship (Zero1): The World Heavyweight Championship is a professional wrestling world heavyweight championship in the Japanese promotion Pro Wrestling Zero1.  It is one of Zero1's top two singles titles, along with the NWA United National Heavyweight Championship.  It was first introduced on December 15, 2007 when Zero1 ended their relationship with the AWA Superstars of Wrestling.  The Superstars of Wrestling champion at the time, Masato Tanaka, was then recognized as the first Zero1 World Heavyweight Champion.  To this day, Zero1 continues to use the AWA title belt, which reads "AWA World Heavyweight Wrestling Champion", to represent the World Heavyweight Championship.  There have been a total of 14 recognized champions who have had a combined 21 official reigns.

MCW Heavyweight Championship: The MCW Heavyweight Championship is a professional wrestling heavyweight championship owned by the MCW Pro Wrestling (MCW) promotion.  The title was created and debuted on October 11, 1998 at a MCW live event.  In 2003, MCW ceased operations; at its last show MCW Last Dance on July 16, the MCW Heavyweight Championship was unified with the FTW Heavyweight and the MEWF Heavyweight Championships, when then–MCW Heavyweight Champion Danny Doring defeated MEWF Heavyweight Champion Romeo Valentino and FTW Heavyweight Champion Chris Chetti.  MCW reopened in 2005 and held its first show on October 1, 2005, titled Fort Meade Wrestling.  The MCW Heavyweight Championship was reinstated on March 26, 2006 at MCW's The Phenomenal Final Four event, where Julio Dinero won a tournament to become the champion.

WWC Universal Heavyweight Championship: The WWC Universal Heavyweight Championship is a professional wrestling world heavyweight championship and the top title contested for in the Puerto Rican professional wrestling promotion, the World Wrestling Council.  The championship was established in July 1982, as the WWC World Heavyweight Championship, when the company was named Capitol Sports Promotions.  The championship received its current name following a match between Carlos Colón (WWC World Heavyweight Champion) and Ric Flair (NWA World Heavyweight Champion) where the "Champion of the Universe" was supposed to be determined.  The first champion was Abdullah the Butcher, who was billed as champion upon the title's creation.  Since being established, the WWC Universal Heavyweight Championship has been held by forty-nine different wrestlers and has also been held up on nineteen occasions and vacated or stripped thirteen times.

UWA World Heavyweight Championship: The UWA World Heavyweight Championship ("Campeonato Mundial peso Completo de UWA" in Spanish) is a professional wrestling world heavyweight championship originally promoted by Universal Wrestling Association (UWA) until it closed in 1995 and since then been defended on the Mexican independent circuit.  In the past the title has been defended in Consejo Mundial de Lucha Libre (CMLL) and Asistencia Asesoría y Administración (AAA) when the champion worked for those companies.  Lou Thez was the first UWA World Heavyweight champion, having been awarded the title after wrestling Mil Mascaras to a draw on the very first UWA show.  El Canek has held the Championship the most times, 15 reigns all in all, 13 of those before the UWA closed.  Canek is also the champion that kept the UWA World Heavyweight Championship active after the UWA closed.  Dr. Wagner, Jr. is the current UWA World Heavyweight champion having defeated Canek on June 18, 2004.  Dr. Wagner, Jr. currently works regularly for AAA and they acknowledge the title, having shown him with the belt on numerous occasions.

IWGP Junior Heavyweight Championship: The IWGP Junior Heavyweight Championship is a professional wrestling junior heavyweight championship owned by the New Japan Pro-Wrestling (NJPW) promotion.  "IWGP" is the acronym of NJPW's governing body, the International Wrestling Grand Prix.  The title was introduced on February 6, 1986, at a NJPW show.  Only wrestlers under the junior heavyweight weight-limit may hold the championship.  NJPW currently controls two junior heavyweight championships: the IWGP Junior Heavyweight Championship and the IWGP Junior Heavyweight Tag Team Championship.  The weight-limit for the tag team title is 100 kg ; it is assumed that this title has the same weight-limit.  From August 5, 1996, until November 5, 1997, the title was part of the J-Crown, or J-Crown Octuple Unified Championship.  The J-Crown was an assembly of eight different championships from several different promotions.  It was created on August 5, 1996, when The Great Sasuke won an eight-man tournament.  The IWGP Junior Heavyweight Championship, the British Commonwealth Junior Heavyweight Championship, the NWA World Junior Heavyweight Championship, the NWA World Welterweight Championship, the UWA World Junior Light Heavyweight Championship, the WAR International Junior Heavyweight Championship, the WWA World Junior Light Heavyweight Championship, and the WWF Light Heavyweight Championship were the eight championships that were involved.  On November 5, 1997, then-champion Shinjiro Otani vacated all J-Crown belts but the IWGP Junior Heavyweight Championship after the World Wrestling Federation (WWF) retook control of its Light Heavyweight title, effectively ending the J-Crown.  Being a professional wrestling championship, the title is won as a result of a predetermined outcome.

List of GFW Global Champions: The GFW Global Championship is a professional wrestling world heavyweight championship owned by the promotion Global Force Wrestling (GFW), formerly Total Nonstop Action Wrestling (TNA).  From June 2002 to May 2007, TNA used the NWA World Heavyweight Championship as their primary championship due to an agreement with the National Wrestling Alliance (NWA).  On May 13, 2007, the NWA abruptly ended the arrangement and retrieved control of the NWA World Heavyweight Championship.  On the same night, TNA were set to host their annual Sacrifice pay-per-view event, in which the NWA World Heavyweight Championship was to be defended by then-champion Christian Cage against Kurt Angle and Sting in a three-way match.  Angle won the match and on the following episode of TNA's television program "Impact! " on May 17, was declared the new TNA World Heavyweight Champion.  He was stripped of the championship later in the program, with Management Director Jim Cornette citing a problematic finish to the title match.  The ownership of the championship was decided on June 17, 2007 at TNA's Slammiversary event in a King of the Mountain match involving Angle and Cage along with A.J. Styles, Chris Harris and Samoa Joe, which Angle won.

James J. Corbett: James John "Gentleman Jim" Corbett (September 1, 1866 – February 18, 1933) was an American professional boxer and a former World Heavyweight Champion, best known as the man who defeated the great John L. Sullivan.  Despite a career spanning only 20 bouts, Corbett faced the best competition his era had to offer; squaring off with a total of 9 fighters who would later be enshrined alongside him in the International Boxing Hall of Fame.

Supporting paragraphs: Fitzsimmons vs. Sharkey James J. Corbett
Answer: "Gentleman Jim"