The IWGP Heavyweight Championship was a professional wrestling world heavyweight championship used by the Inoki Genome Federation (IGF) promotion. The title shares its name with New Japan Pro Wrestling's (NJPW) IWGP Heavyweight Championship, from which it split due to a decision made by IGF and NJPW founder Antonio Inoki. "IWGP" is the abbreviation of NJPW's fictional governing body, the International Wrestling Grand Prix.
During the title's history, IGF recognized it as the official IWGP Heavyweight Championship, continuing the history of the title after an error made by NJPW in Inoki's eyes. NJPW recognized the title as the IWGP 3rd Belt Championship, a championship that was merely represented by a previous version of the IWGP Heavyweight Championship's title belt. The title was briefly used in the Total Nonstop Action Wrestling (TNA) promotion, which recognized it as the IWGP Heavyweight Championship.
As a professional wrestling championship, the title was won via a scripted ending to a match or awarded to a wrestler because of a storyline. The inaugural champion was Brock Lesnar, who was the reigning IWGP Heavyweight Champion before being stripped of the title due to issues with NJPW. IGF recognized him as the official IWGP Heavyweight Champion afterwards. All title changes occurred at IGF or NJPW-promoted events. There were a total of three reigns among three wrestlers during the title's brief history before being unified with the IWGP Heavyweight Championship.
On October 8, 2005, at New Japan Pro Wrestling's (NJPW) Toukon Souzou New Chapter event in Tokyo, Japan, Brock Lesnar defeated Kazuyuki Fujita and Masahiro Chono in a Three Way match for the IWGP Heavyweight Championship. He held the title for 280 days, having three successful defenses, until he failed to show up for a scheduled title defense. NJPW thus stripped Lesnar of the championship on July 15, 2006. Lesnar cited visa issues along with NJPW owing him compensation for his reasons at failing to appear at the planned title defense. After this series of events, NJPW founder Antonio Inoki left NJPW and created a new promotion, the Inoki Genome Federation (IGF). Inoki then recognized Lesnar as the IWGP Heavyweight Champion due to Lesnar never having lost the championship in a match and Lesnar still maintaining physical possession of the title belt. NJPW recognized Lesnar as the IWGP 3rd Belt Champion and not the IWGP Heavyweight Champion, maintaining their stance on having stripped him of the title in 2006.
On June 29, 2007, IGF held its debut show with Lesnar defending the IWGP Heavyweight Championship against Kurt Angle in the main event. Angle defeated Lesnar to win the championship at the show with Angle going on to appear in the American Total Nonstop Action Wrestling (TNA) promotion with the physical title belt. TNA also referred to the title belt as the IWGP Heavyweight Championship in the same manner as the IGF, recognizing Angle as the official IWGP Heavyweight Champion. NJPW did not recognize Angle as the IWGP Heavyweight Champion, instead it viewed Angle as the second IWGP 3rd Belt Champion.
Angle went on to have two successful defenses as champion. His first defense came in TNA in a feud against Samoa Joe. Angle first appeared with the title belt in TNA on the July 5, 2007, episode of TNA's television program TNA Impact!. The title belt became relevant to the storyline rivalry between Joe and Angle heading into TNA's Hard Justice pay-per-view (PPV) event. Leading up to TNA's Victory Road PPV event on July 15, 2007, TNA X Division Champion Joe and TNA World Heavyweight Champion Angle teamed together to face TNA World Tag Team Champions Team 3D (Brother Devon and Brother Ray) in a Tag Team match with the stipulation being whoever scored the pinfall or submission for their team won the championship of the person pinned or made to submit. Joe pinned Brother Ray in the bout, thus winning the World Tag Team Championship for himself and a partner of his choosing. Joe chose to hold the title alone and challenged Angle to a Winner Take All match at Hard Justice for the TNA World Heavyweight, TNA X Division, TNA World Tag Team, and the IWGP Heavyweight Championships on the July 19 2007, episode of Impact!. Angle accepted the match, with Joe and Angle facing at Hard Justice on August 12, 2007 in Orlando, Florida for all of the titles. Angle defeated Joe at the event to win the TNA World Tag Team and TNA X Division Championships, while retaining the TNA World Heavyweight and IWGP Heavyweight Championships. Afterwards, TNA slowly fazed out the IWGP Heavyweight Championship with Angle going on to defend the title at IGF and NJPW promoted shows, with the title being referred to as both the IWGP Heavyweight Championship and the IWGP 3rd Belt Championship.
Angle's second defense of the title was at NJPW's Wrestle Kingdom II in Tokyo Dome event on January 4, 2008, where he defeated former NJPW recognized IWGP Heavyweight Champion Yuji Nagata to retain the IWGP 3rd Belt Championship. Angle's last defense was against then NJPW recognized IWGP Heavyweight Champion Shinsuke Nakamura in a unification match on February 17, 2008 at NJPW's Circuit 2008 New Japan ISM event where the winner would be the unified IWGP Heavyweight Champion. Angle lost the match, thus ending the existence of the IGF recognized IWGP Heavyweight Championship. IGF later introduced another title five years later with the IGF Championship on December 31, 2013.