Naoya Inoue continued cementing his legacy among boxing's greats with his latest victory in Tokyo.
The Japanese sensation dealt with Marlon Tapales within 10 rounds, adding the IBF and WBA super bantamweight titles to his WBC and WBO straps to become the undisputed king at 122 pounds.
It came just a year after cleaning up in the bantamweight division, meaning "The Monster" became the second male fighter in the four-belt era to claim all the gold in two different divisions, after Terence Crawford did the same via his win over Errol Spence Jr. earlier in 2023.
In the female game, Claressa Shields had made undisputed history before Crawford, while Katie Taylor's recent revenge mission against Chantelle Cameron saw her match the feat.
But what does it mean to be undisputed in boxing’s complicated landscape of multiple belts and champions? Allow us to explain.
MORE: Katie Taylor avenges loss to Chantelle Cameron with points win
What is an undisputed champion? Are there four or five belts?
The haul of belts Crawford completed at T-Mobile Arena are the parts required to become an undisputed champion. The WBC, WBA, IBF and WBO are the four major recognised belts in boxing.
This has not always been the case. The WBC and WBA are long-established titles, meaning undisputed champions were more common in previous eras.
Crawford and Spence’s showdown earned plenty of deserved comparisons to the seismic 1981 meeting between Sugar Ray Leonard and Thomas Hearns. Leonard was the reigning WBC welterweight champion and took the WBA belt off Hearns with a dramatic 14th-round stoppage, becoming undisputed.
The IBF entered the picture as a major player in the 1980s, while the WBO’s ascent to the top table was somewhat staggered. Although WBO title meetings such as the British blockbusters between Chris Eubank and Nigel Benn conferred legitimacy in certain weight classes, in others, it amounted to little more than a meaningless trinket.
For example, when WBC heavyweight champion Lennox Lewis met WBA and IBF ruler Evander Holyfield in their huge two-fight series in 1999, it was billed and recognised as an undisputed showdown. While the IBF quickly entered the elite conversation by recognising existing WBA and WBC champions as its No.1 fighters, the WBO’s decision after its 1988 formation to allow lesser-known fighters to compete for its vacant titles meant a longer route to the top table.
At heavyweight, WBO champions Michael Moorer, Riddick Bowe and Henry Akinwande vacated the belt to pursue the more established titles. However, the likes of Naseem Hamed, Joe Calzaghe, Oscar De La Hoya and Wladimir Klitschko were among those to help build the organisation’s prestige. In 2004, the WBC began naming WBO champions in its rankings and the IBF recognised its rival in 2007.
Below the big four, the IBO is the most notable world title today but is not considered in the undisputed conversation. The proliferation of subsidiary and alternative titles within the big four (regular, super, diamond, franchise, emeritus — take your pick) has also muddied the waters. To be considered the undisputed champion, a fighter must be in possession of the “full” world title belt from each of the WBC, WBA, IBF and WBO.
MORE: Boxing pound-for-pound rankings
Eagle-eyed fans will have noticed a fifth piece of hardware on Crawford’s shoulders in Las Vegas — the celebrated Ring Magazine belt. While not a sanctioning body title, the championship awarded by the American boxing publication is generally revered because it cuts through the complications of the alphabet belt era as a single title that recognises the best fighter in each weight class.
Crawford became the first Ring Magazine welterweight champion since Floyd Mayweather Jr. in 2015 because the fight between himself and Spence was between the recognised No.1 and No.2 in the division.
As such, The Ring title tends to complement an undisputed haul rather than undermine a champion’s claims — something that has become notable over the recent past in men’s and women’s boxing when undisputed champions have become more commonplace, with promoters, broadcasters and fighters alike recognising both the prestige and commercial advantages of having a single, unified champ.
Full list of men's undisputed champions
Below is the list of undisputed men's world champions in the four-belt era
| Name | Division | Date |
| Bernard Hopkins | Middleweight | September 2004 |
| Jermain Taylor | Middleweight | July 2005 |
| Terence Crawford | Super Lightweight | August 2017 |
| Oleksandr Usyk | Cruiserweight | July 2018 |
| Josh Taylor | Super Lightweight | May 2021 |
| Canelo Alvarez | Super Middleweight | November 2021 |
| Jermell Charlo | Super Welterweight | May 2022 |
| Devin Haney | Lightweight | June 2022 |
| Naoya Inoue | Bantamweight | December 2022 |
| Terence Crawford | Welterweight | July 2023 |
| Naoya Inoue | Super bantamweight | December 2023 |
Crawford became the first men's two-weight undisputed champion in the four-belt era by beating Spence. His fellow pound-for-pound high-flyer Naoya Inoue joined him, having stepped up to super bantamweight to stunningly dethrone WBC and WBO champion Stephen Fulton, then IBF and WBA champion Marlon Tapales.
Jermain Taylor remains the only man to win an undisputed title as a challenger to a champion holding all four of the belts when he defeated the great Bernard Hopkins in July 2005.
Three-belt champion Oleksandr Usyk is in contention for the undisputed heavyweight crown to his cruiserweight efforts in February 2024. After countless attempts at the negotiating table failed, he is now set to face Tyson Fury in one of the biggest fights in the history of the sport.
Full list of women's undisputed champions
| Name | Division | Date |
| Cecilia Braekhus | Welterweight | September 2014 |
| Claressa Shields | Middleweight | April 2019 |
| Katie Taylor | Lightweight | June 2019 |
| Jessica McCaskill | Welterweight | August 2020 |
| Claressa Shields | Super Welterweight | May 2021 |
| Franchon Crews-Dezurn | Super Middleweight | April 2022 |
| Claressa Shields | Middleweight | October 2022 |
| Chantelle Cameron | Super Lightweight | November 2022 |
| Amanda Serrano | Featherweight | February 2023 |
| Alycia Baumgardner | Super Featherweight | February 2023 |
| Savannah Marshall | Super Middleweight | July 2023 |
| Katie Taylor | Super Lightweight | November 2023 |
Claressa Shields has been the dominant force of the women's undisputed era, becoming a two-time middleweight champion when she defeated Savannah Marshall in October 2022. Shields was undisputed at 154lbs after beating Marie Eve Dicaire a year earlier.
Marshall imitated Jermain Taylor's feat of beating a reigning four-belt champion when she dethroned Franchon Crews-Dezurn to become undisputed at super middleweight. Jessica McCaskill did likewise when she beat long-reigning welterweight queen Cecilia Braekhus in August 2020.
McCaskill's bid to join Shields as a two-weight undisputed champion came unstuck when she lost to Chantelle Cameron in a battle for supremacy at 140lbs in November 2022. Cameron defended those belts successfully against undisputed lightweight champion Katie Taylor earlier this year, the first meeting between two reigning undisputed champions in the four-belt era.
In November 2023, Taylor avenged her first professional defeat and picked up all the super lightweight belts when she outpointed Cameron in a direct rematch.
