When the UFC made its debut 30 years ago, it was very different to the slick, refined operation we have today.
There were minimal rules, and perhaps most notably, no weight classes. It wasn't until UFC 12 in 1997 that weight classes were introduced, and it wasn't until as recently as 2006 that the lighter weight classes were introduced following the UFC's acquisition of World Extreme Cagefighting, which boasted champions including Jose Aldo, Urijah Faber, and Dominick Cruz.
The UFC now has eight weight divisions for men and four for women.
Here are all of the weight classes and their current champions.
Record: 27-1 (1 NC)
Next fight: TBC
After Francis Ngannou left the UFC, vacating his title, the heavyweight division was awaiting a new champion.
Former light-heavyweight champion Jon Jones finally made the step up to take on former challenger Ciryl Gane at UFC 285 on 4th March, winning via first-round guillotine.
Jones was set to fight arguably the UFC's greatest ever heavyweight in Stipe Miocic, but with Jones pulling out through injury, Tom Aspinall will face Sergei Pavlovich for the interim title at UFC 295.
Next fight: TBC
When Jon Jones was ruled out of his title fight with Stipe Miocic, and interim bout between Tom Aspinall and Sergei Pavlovich was set up.
Aspinall won via first-round knockout to claim the interim title, and will hope for a unification fight with Jones in 2024.
Next fight: TBC
Jiri Prochazka's injury threw the division into turmoil in November 2022, vacating his title, with would-be challenger Glover Teixeira also pulling out of their proposed fight. Magomed Ankalaev and Jan Blachowicz fought out a draw, leaving the title without a holder, before Jamahal Hill beat Teixeira at UFC 283.
Hill suffered an injury of his own, leaving the division without a champion again, but with Alex Pereira's win at UFC 291, he found himself next in line to take on former champion Prochazka for the vacant belt at UFC 295.
Pereira won with a second-round TKO and should Magomed Ankalaev win his rematch with Johnny Walker in January, the Russian may be Pereira's next opponent.
Next fight: Dricus du Plessis (UFC 297, 20th January)
Filed alongside Georges St-Pierre losing to Matt Serra and Ronda Rousey losing to Holly Holm, Sean Strickland's shock victory over Israel Adesanya will forever go down as one of the UFC's greatest upsets.
The UFC weren't even willing to make the fight but were left with no choice when potential candidates turned the bout down. And it was no fluke; Strickland put Adesanya down in the first and was the better man throughout, deservedly out-pointing the champion.
Adesanya said he'd be taking an extended break from MMA, leaving the door open for Dricus du Plessis - a perfect 6-0 since joining the UFC - to challenge the new champion at UFC 297.
Record: 21-3 (1 NC)
Next fight: Colby Covington (UFC 296, 16th December)
For so long one of the hard-luck tales of the UFC, Leon Edwards finally got his title shot against P4P number one Kamaru Usman, winning with a devastating knockout with a minute left of the fight.
Usman had looked nigh-on unbeatable during his title reign, and the pair met again at UFC 286 on 18th March, with Edwards winning via unanimous decision.
Two-time challenger Colby Covington will get a third crack at the title when he fights Edwards at UFC 296 on 16th December.
Next fight: TBC
Islam Makhachev had spent a long time on the outside looking in as the UFC's most competitive division battled it out for the title, with Charles Oliveira eventually establishing himself as the top dog, but Makhachev was always waiting in the wings, looking like a champion in waiting.
The pair met, with Makhachev capturing the title, and he made his first defence against Alexander Volkanovski at UFC 284 on 12th February, narrowly out-pointing the Australian.
Makhachev's next defence came at UFC 294 against Volkanovski, after Charles Oliveira was forced to pull out through injury. Makhachev stopped his Australian opponent in the first round to claim a devastating KO victory.
Oliveira is set to get a rematch, though a date hasn't yet been set.
Next fight: Ilia Topuria (UFC 297, 20th January)
Alexander Volkanovski claimed the featherweight title in 2019 and has clung on like a rabid dog ever since. He out-pointed Max Holloway to claim the belt, doing so two more times (Holloway, remember, has only been stopped once in 30 MMA fights), also beating Brian Ortega and the Korean Zombie.
The featherweight division isn't stacked with potential contenders, and the Aussie has beaten the top contender three times, so Volkanovski stepped up to lightweight in an attempt to become a two-weight world champion against Islam Makhachev, losing via decision.
Volkanovski defended his title via TKO to unify the division against Rodriguez at UFC 290. He then attempted to become two-weight champion facing Makhachev again for the lightweight title at UFC 294, but was knocked out in the first round of that clash, suffering the third defeat of his MMA career.
Volkanovski's next fight will be back at featherweight against Ilia Topuria at UFC 297 on 20th January.
Record: 17-1 (1 NC)
Next fight: Marlon Vera (UFC 299, 9th March)
Now one of the bona fide superstars of the sport, 'Sugar' Sean O'Malley took ownership of the bantamweight title in style by knocking out Aljamain Sterling at UFC 292.
O'Malley has been on the up for a number of years, but his ability to become world champion was still up for debate right up until his breath-taking stoppage of Sterling.
O'Malley, who has gained a strong following thanks to his natural charisma and flashy appearance, will make his first defence against Marlon Vera next March.
Next fight: Brandon Royval (UFC 296, 16th December)
After years of Demetrius Johnson dominance, Henry Cejudo became the king of the 125lbs division before hanging up the gloves, leaving a void at flyweight. Brandon Moreno and Deiveson Figueredo fought out a quadrilogy, with Moreno finally coming out on top to settle the score once and for all.
After back-to-back Performance of the Night contests, Alexandre Pantoja moved up to #2 in the flyweight rankings, setting up a third fight with Moreno since 2016.
Panjota won by split decision to record a third win over Moreno at UFC 290, and will make his first title defence against Brandon Royval at UFC 296 in a rematch of their 2021 bout, which Pantoja won by submission.
Following Amanda Nunes's retirement, Dana White suggested that women's featherweight division may be retired with the former champion. There's never been sufficient activity within the division, with Nunes only defending the title twice since capturing it in 2018.
After the Ronda Rousey era came the Amanda Nunes era. A total of six title defences across two reigns saw Nunes match Rousey's record reign, but after her win over Irene Aldana, the Lioness hung up the gloves, leaving a gaping hole in the women's division, with Julianna Pena - the only woman to beat Nunes in a title fight - surely next in line for another crack at the title.
Next fight: TBC
While Amanda Nunes dominated the heavier women's weight classes, the 125lbs division belonged to Valentina Shevchenko since 2018.
As invincible as Nunes looks at 135, Shevchenko looked her equal at 125, making seven straight title defences before running into Alexa Grasso at UFC 285, losing via a fourth-round face crank.
The pair faced off again on 16th September at UFC Fight Night 227, with the pair fighting out a razor-thin draw, and there are sure to be calls for a third fight between the pair.
Next fight: TBC
After losing her crown to Rose Namajunas, and controversially losing the rematch, Zhang won her next two fights to regain the title against Carla Esparza.
Zhang then beat Amanda Lemos at UFC 292, with fans now eyeing up a trilogy fight between her and Rose Namajunas.