On Saturday night, two undisputed champions will clash for the first time in boxing's four-belt era when undisputed junior middleweight champion Jermell Charlo moves up two divisions to challenge undisputed super middleweight champion Saul "Canelo" Alvarez in a Showtime pay-per-view main event.
Alvarez knocked out Caleb Plant in 2021 to lock down his fourth world title at super middleweight. He has twice defended his undisputed status, taking decision wins over Gennadiy Golovkin and John Ryder to retain his titles.
Charlo first battled to become undisputed champion in 2021. In an attempt to add Brian Castano's WBO junior middleweight title to his own WBA, WBC and IBF belts, Charlo was forced to accept a split draw. In the 2022 rematch, Charlo scored a 10th-round stoppage to become undisputed. He has not fought since and his world titles are not on the line on Saturday night, though he will officially be stripped of his WBO title, and interim champion Tim Tszyu will be promoted to world champion, the moment Charlo is announced as champion during pre-fight introductions.
Here's a look at every undisputed titleholder of the four-belt era, which began in 2004.
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Bernard Hopkins: Middleweight (2004-2005)
Hopkins became the first undisputed champion of the four-belt era when he knocked out Oscar De La Hoya in 2004 to earn all of the middleweight belts. His reign lasted less than a year, however, as he lost a surprise split decision to Jermain Taylor in the first of two bouts between the men.
Jermain Taylor: Middleweight (2005)
Taylor's upset victory via split decision over Bernard Hopkins made him the undisputed champion at middleweight, but he never made a defense of all four belts. He vacated his IBF title in order to facilitate his rematch with Hopkins six months later, which he won by unanimous decision.
Terence Crawford: Junior welterweight (2017)
Crawford's first successful four-belt unification came at the junior welterweight division when he knocked out Julius Indongo in the third round of their 2017 contest. His reign ended shortly thereafter, however, as he vacated the IBF title over a dispute about the mandatory challenger and his eventual move up to 147 pounds.
Oleksandr Usyk: Cruiserweight (2018-2019)
Usyk solidified himself as one of the best fighters of this generation with a brilliant run during the World Boxing Super Series tournament. In the final, he won a unanimous decision over Murat Gassiev to become the undisputed king at 200 pounds. He held all four belts there until 2019, when he vacated to move up to heavyweight.
Josh Taylor: Junior welterweight (2021-2022)
Taylor is the second fighter to fully unify the 140-pound division, joining Crawford in that exclusive club. He did so by earning an impressive unanimous decision victory over Jose Ramirez in 2021. He then made one successful defense of all four belts before his WBA title was stripped over a dispute about a mandatory challenger.
Canelo Alvarez: Super middleweight (2021-current)
Alvarez is a four-division world champion, but the only one he has become undisputed in is super middleweight. He did so in 2021 when he scored a TKO victory over Caleb Plant in their unification bout. He has since defended the titles against Gennady Golovkin in the third fight of their trilogy, and most recently versus John Ryder. He's expected to face another undisputed king in his next fight this year in Jermell Charlo.
Jermell Charlo: Junior middleweight (2022-current)
Charlo's first attempt at claiming all four junior middleweight belts was unsuccessful, as his fight against Brian Castano in 2021 was scored a draw. When the two squared off for a rematch in 2022, however, Charlo left nothing to the judges and completely unified the division via a knockout victory.
Devin Haney: Lightweight (2022-current)
Haney made the brave decision to travel all the way to Australia in 2022 to take on George Kambosos for all four lightweight straps. The risk was worth the reward, as Haney won by unanimous decision. Since then he has successfully defended the belts against Kambosos in their rematch, and most recently outpointed Vasiliy Lomachenko.
Naoya Inoue: Bantamweight (2022-2023)
Inoue, better known as "The Monster," defeated Paul Butler in 2022 to finally become the undisputed bantamweight champion, more than three years after he first earned a belt in the division. He did not make a defense, however, as he vacated all four belts to move up to super bantamweight, where he currently holds two titles.
Terence Crawford: Welterweight (2023-current)
Crawford won his first welterweight title in 2018 by defeating Jeff Horn, and defended that WBO belt six times before he finally got a chance to cross the street and take on Errol Spence for all four belts. He made shockingly easy work of Spence in that long-awaited showdown, and is now the undisputed welterweight king.
Cecilia Braekhus: Welterweight (2014-2020)
In March 2009, Braekhus beat Vinni Skovgaard to win the WBA and WBC titles. That was just Barekhus' 11th professional fight. Three fights later, she added the WBO belt with a decision win over Victoria Cisneros. Braekhus would then defend those three titles 11 times before beating Ivana Habazin to secure the IBF title and undisputed status. She would add another 10 wins before finally suffering the first loss of her career, dropping the titles to Jessica McCaskill.
Katie Taylor: Lightweight (2019-current)
Taylor is an all-time great. She won her first title in her seventh career fight, beating Anahí Ester Sanchez to claim the WBA lightweight belt. She successfully defended that belt against McCaskill before defeating Victoria Bustos to win the IBF belt. Four fights later, Taylor added the WBO belt with a win over Rose Volante. Her next outing was the moment she became undisputed by winning the WBC belt against Delfine Persoon. Taylor has made seven defenses of her four world titles, including against future undisputed featherweight champion Amanda Serrano. Her only career loss came in her most recent fight, her bid to move up in weight to become a two-division undisputed champion against Cameron.
Claressa Shields: Middleweight (2019-current)
Shields' claim that she's the "G.W.O.A.T." (Greatest Woman of All Time) is hard to dispute given her myriad accomplishments inside the squared circle. Shields' first professional win came against one of the women on this list, Franchon Crews-Dezurn, and she was winning titles almost immediately after her career began. While Sheilds was happy to move between divisions seeking challenges and titles, middleweight was the division into which Shields originally settled. After collecting some belts at super middleweight, Shields moved to middleweight where she defeated Hanna Gabriels in June 2018 to win the WBA and IBF titles. A win over Hannah Rankin followed to add the WBC belt. Shields became undisputed in April 2019, beating Christina Hammer for the WBO strap.
Jessica McCaskill: Welterweight (2020-2022)
McCaskill did not require a long road to get to undisputed status. After unifying the WBA and WBC titles at junior welterweight, she made the move up to welterweight and immediately challenged Braekhus and won all four world titles. She successfully defended the belts in the rematch and then twice more before attempting to jump up in weight to move back down in weight and become undisputed against Chantelle Cameron. Cameron won the bout by decision. Her move in weight divisions led to the welterweight titles being split.
Claressa Shields: Junior middleweight (2021-current)
After becoming undisputed at middleweight -- which came after being unified at super middleweight -- Shields immediately looked to the division below to start grabbing more gold. In January 2020, Shields beat Ivana Habazin to win the WBC and WBO titles. In her next fight, she defeated Marie-Eve Dicaire to add the WBA and IBF belts, becoming the first boxer in history to have been undisputed four-belt world champion in two divisions.
Franchon Crews-Dezurn: Super middleweight (2022-2023)
Rare is the fighter who loses their pro debut to a legend but still makes history of their own. Crews-Dezurn lost to Shields in her debut match but won the WBC super middleweight title four fights later, beating Maricela Cornejo. Two fights later, Crews-Dezurn fought Cornejo again, collecting the vacant WBO title with another win. In April 2022, Crews-Dezurn added the final two super middleweight titles with a win over Elin Cederroos. Crews-Dezurn would drop her titles in her next fight, losing to Savannah Marshall.
Chantelle Cameron: Junior welterweight (2022-current)
Cameron won the WBC title in October 2020 with a win over Adriana Araújo. Two fights later, the IBF title was added to her collection after she defeated Mary McGee. When McCaskill moved down in weight for her fight with Cameron, the vacant WBA and WBO titles were added to the mix. Cameron's win made her undisputed, a status she retained when she defeated undisputed lightweight champion Katie Taylor by majority decision in May.
Amanda Serrano: Featherweight (2023-current)
Serrano is another fresh face among the undisputed ranks. She failed in her first bid to become a four-belt champion when she moved up to face Taylor in the biggest fight in women's boxing history. While Serrano, already a unified featherweight champion, came up short, she was one half of a legendary fight. After the Taylor fight, Serrano beat Sarah Mahfoud to add the IBF title to her WBC and WBO belts. One fight later, in her most recent outing, Serrano beat Erika Cruz to win the WBA belt and become a four-belt champion.
Savannah Marshall: Super middleweight (2023-current)
Marshall lost in her first big at undisputed glory, losing an October 2022 bout with Claressa Shields at middleweight. That fight was highly anticipated as Marshall was the only fighter to ever defeat Shields, doing so in an amateur bout. Despite losing a very entertaining bout to Shields, Marshall went right back to seeking to become undisputed champ. She did just that in July, taking a decision over Crews-Dezurn to win the four super middleweight world championships.
Alycia Baumgardner: Super featherweight (2023-current)
Baumgardner's journey to undisputed has a nice element of a story coming full circle. Baumgardner suffered her first loss in July 2018, dropping a split decision against Christina Linardatou. It would take until November 2021 before she would hold a world title, stopping Terri Harper in four rounds to win the WBC super featherweight belt. An October 2022 split decision win over Mikaela Mayer added the WBO and IBF belts to Baumgardner's collection. In February, Baumgardner completed her journey to undisputed with a win over Elhem Mekhaled. In July, Baumgardner made her first defense as undisputed champion, beating Linardatou to avenge her sole career defeat.