Twenty-five years into the experiment that promised to determine the most effective martial art, the question is all but expired. Evolution has repeatedly proven that a melding of existing styles and a willingness toward adaptability will continually redefine the potent methods of the moment. It is always shifting, changing, developing; a living art form.

In that quarter-century, the UFC has welcomed thousands of fighters to the cage, all with the intent of rising to the top. A scant few have gotten there, able to call themselves a UFC champion. But an even smaller subset remain the best of the best; the most important fighters ever to step foot into the Octagon. While any list is subjective, in considering the measures necessary for inclusion, we focused on criteria including total body of work, strength of schedule, accomplishments, historical importance, and head-to-head results.

With the UFC celebrating its silver anniversary on Nov. 10, this multi-part series pays tributes to the key names that pushed the promotion’s rise, starting with Nos. 25-16.

When Robbie Lawler returned to the UFC in early 2013, more than eight years after his original UFC run ended, expectations were tempered. Lawler had finished a Strikeforce stint looking like his best days were behind him. Nearing 31 years old at the time, Lawler had won only three of his eight Strikeforce bouts.

His Octagon comeback, however, sparked a personal renaissance. Lawler dipped back down to welterweight and refined his approach in the cage to give his technical brawling style maximum opportunities within each bout. The result was magic. Lawler authored memorable wins over Josh Koscheck and Rory MacDonald before capturing the championship in December 2014 by edging Johny Hendricks. His rematch with MacDonald the next year, in which Lawler retained the belt, stands as one of the most grueling, visceral displays of mixed martial arts ever.

He successfully defended the belt twice, and still cuts a fierce presence at age 36. Few who watch him will ever forget the look of fiendish delight he often reflects at the start of a match, or the intensity he radiates.

The ability to find success in multiple eras nearly a decade apart is rare; among that small group, achieving a UFC championship in a second act sets Lawler apart.

The argument for Dominick Cruz on the all-time top 25 list is a simple one: He is the best bantamweight that MMA has ever seen. While Cruz has only logged six fights in the UFC, largely due to a rash of injuries that have limited his activity, he remains the division’s all-time standard-bearer, even as T.J. Dillashaw closes in fast.

Cruz, after all, beat Dillashaw straight-up, even though the split-decision victory was in some quarters controversial.

Utilizing an unorthodox approach that prizes constant movement and complex footwork, Cruz fashioned a style that emphasized the best of his traits while making him an elusive target for opponents. Aside from beating Dillashaw, he has wins over Demetrious Johnson, Urijah Faber (twice) and Takeya Mizugaki.

The last of those is looked upon by many as one of the great all-time MMA comebacks. After being sidelined for three years for various injuries including two torn ACLs and a torn groin, Cruz savaged the perennial and durable contender Mizugaki, mowing through him in just 61 seconds. That led to his Dillashaw match and a second UFC title reign, making him the first fighter ever to hold that championship twice.

The UFC welterweight championship has historically been the most prestigious and stable belts within the organization, with past holders including the legendary Georges St-Pierre, the great Matt Hughes, and the aforementioned Lawler.

Over the last few years, Tyron Woodley has taken his place alongside those titans with his own lengthy reign, which is over 800 days and counting. Fusing a power wrestling style with blazing speed and crushing power, Woodley has ruled the division, putting names like Lawler, Stephen Thompson, Demian Maia and Kelvin Gastelum on his mantle.

Woodley’s signature victory is unquestionably his title-winning performance. Lawler, who entered the fight looking like MMA’s version of The Terminator, was an outsized favorite, but Woodley made short work of him, dismantling the champion with a laser right hand and ground strikes in less than three minutes.

With four successful title defenses already under his belt, Woodley has an opportunity to further his legacy in 2019 and beyond.

After mowing through Conor McGregor at UFC 229, Khabib Nurmagomedov’s record stands as a gaudy 27-0, with 11 of those wins coming in the UFC. Statistically, that stands as the most impressive start to a UFC career since Royce Gracie christened the Octagon with 11 straight wins to christen the promotion. That’s what kind of a historic run Nurmagomedov has had now, a quarter-century later.

He’s done it largely on the strength of his relentless takedowns and mauling grappling game, drowning his opponents through unshakable tenaciousness. Fighting Nurmagomedov must feel something like trying to unlock a pitbull’s jaw from his target, with every wiggle of resistance only strengthening his grip and resolve. Worse, Nurmagomedov will actively convince you to surrender during the process, often verbally chiding his opponent while battering them.

Nurmagomedov holds a UFC record with 21 takedowns in a single fight, and to date, has only lost a single round in his career, raising the issue of who is capable of ending this kind of dominance.

With a Nevada Athletic Commission disciplinary hearing pending and Tony Ferguson looming, challenges stand ahead, but until now, his resume has been something rarely seen in the UFC: Perfect.

In a career that has spanned well over a decade and resulted in major championships in both the UFC and Strikeforce, Cris Cyborg’s résumé stands on its own. But during the midst of the short-lived but explosive Rousey-mania, she was often the odd woman out, a destroyer overshadowed by a force out of her control.

If there was any benefit to Ronda Rousey’s quick fade out, it was the attention returning to indisputably the best female MMA fighter of all-time. Cyborg has dominated opponents before, during, and after the Rousey era, and still remains the UFC featherweight champion, with recent wins over Yana Kunitskaya, Holly Holm, and Tonya Evinger.

One thing that keeps Cyborg from moving further up the list is her relatively short tenure in the UFC; she debuted in May 2016 at a 140-pound catch weight as she experimented with cutting down to bantamweight, a move she ultimately scrapped when the UFC finally added her division in 2017.

Cyborg has fought six times in the UFC, going 6-0 with five stoppage wins, and has a chance to add a meaningful victory to her ledger when she faces current bantamweight champion Amanda Nunes in December.

No fighter in UFC history has as complicated and lengthy a legacy as Vitor Belfort, whose career spanned three different runs, two ownership groups, two decades, one championship, and a series of PED-related controversies.

While Belfort’s career 15-11 mark in the UFC isn’t eye-popping, his impact in his native Brazil cannot be denied. Belfort at one time was the most popular fighter in the fight-mad country, even eclipsing Anderson Silva. By the time the two squared off at UFC 126 in February 2011, the matchup was billed as Brazil’s “Fight of the Century.” Belfort lost, but his starpower helped open the Brazilian market as one of the UFC’s most dependable.

Belfort originally debuted in the UFC in 1996. Looking like Hercules, he won UFC 12’s heavyweight tournament championship the next year, and drew early comparisons to Mike Tyson.

He didn’t win a UFC title until 2004, and lost it months later. In 2009, he returned for a third run with the promotion, notching major wins over Rich Franklin, Anthony Johnson, Luke Rockhold, and Dan Henderson. However, several of his wins came during a period when therapeutic use exemptions for testosterone replacement therapy were in vogue, with Belfort at the vanguard of the movement. That cast some shadows on his achievements, along with failed tests in 2012 and 2014. His impact was unquestionable; the same can’t be said for his method of achievement.

Widely considered to be one of the most polarizing names in UFC history, Michael Bisping fashioned a career that always seemed to fall just short of the ultimate goal of winning a UFC championship.

That changed in 2016, when suddenly gifted with a middleweight title shot, he stunned Luke Rockhold with a crushing left hook. It put a well-deserved cap on an excellent 12-year career that saw him go from abrasive newcomer to venerated veteran.

During his lengthy run, Bisping notched 20 wins — tied for the most in UFC history — including victories over two of the best middleweights ever: Anderson Silva and Dan Henderson.

Bisping should also be remembered for his courage. In 2013, while fighting Vitor Belfort, Bisping suffered a retinal detachment of his right eye, a problem that plagued him through the rest of his career and has resulted in at least five surgeries.

That Bisping won the championship and authored his best in-cage moments after the injury says all you need to know about his ambition and grit.

18. Ronda Rousey

Ronda Rousey will forever be viewed as the UFC’s supernova, who arrived on the scene nearly fully formed, exploded in worldwide popularity and then disappeared, leaving a trail in her wake.

Inside the cage, Rousey’s merits as an all-time UFC great can be debated, if only for the brevity of her career. She went 6-2 in eight fights spanning just three-and-a-half years, including a series of blistering, sub-one-minute victories over Alexis Davis, Cat Zingano, and Bethe Correia. As it turned out though, the height of her powers was also the beginning of the end, as Rousey was crushed by Holly Holm in her next time out, and again knocked out by Amanda Nunes a year later before calling it quits at the age of 29.

But Rousey’s impact on the game is beyond question. The first bonafide female combat sports pay-per-view phenom, Rousey parlayed her success into major movie acting roles, talk show appearances, and magazine spreads. Her celebrity in turn lifted the organization through drawing power, headlining three events that drew over 900,000 buyers, including two that drew 1.1 million each.

It’s not quite fair to look at Cain Velasquez’s record of achievement, which includes two UFC heavyweight championships, and wonder what might have been. Still, it’s hard not to.

When he was healthy, Velasquez might have been the most dominant heavyweight the sport has ever seen.

Velasquez’s greatest gift was his unrivaled conditioning. Few big men could match his furious pace, which often came in the form of relentless wrestling attacks and consistent forward combinations. Opponents were simply overwhelmed from the opening minutes, and could never find time to recover.

When he crushed Brock Lesnar at UFC 121, it seemed that a long reign would be in store, but Velasquez, hiding an injured rotator cuff, was knocked out by Junior dos Santos in just 64 seconds the next fight. To his credit, he rebounded, recapturing the belt by decimating dos Santos in a rematch, and later winning the rubber match in similarly dominant style to emphatically settle the question of which was the greater fighter. Velasquez has overwhelmed several other notables including Antonio Rodrigo Nogueira, Antonio Silva, and Travis Browne, but since the start of 2014, he’s been able to compete only twice.

Now 36, Velasquez is reportedly clear to make his return after a two-year hiatus, and with thoughts of a third championship.

A man with a legacy well past his record of achievement, Ortiz played a key role in keeping interest in the UFC alive at a time when the promotion was facing significant business struggles.

One of the first fighters to realize the value inherent in personality to audiences, Ortiz cultivated fans with his brazen trash talk, his coarse gravedigger celebration and his aggressive style.

Ortiz was one of the promotion’s first dominant champions, winning the light heavyweight belt in 2000 against a young Wanderlei Silva, then defending it four straight times as the setup to his fight against Ken Shamrock in November 2002, a fight that many historians consider a key turning point in ensuring the long-term survival of the UFC — and perhaps with it, the sport itself. Ortiz and Shamrock spent weeks trashing each other in the media, and the fight drew a near-sellout crowd to the MGM Grand Garden Arena, as well as 100,000 pay-per-view buys, a number far above its average at the time. Ortiz’s corner stoppage victory helped make him a superstar in the sport, and a building block for the promotion for years to come.

In the cage, Ortiz holds career wins over Vitor Belfort, Forrest Griffin, and Evan Tanner, but became perhaps best known for his rivalry with Chuck Liddell, which in 2006 produced UFC 66, an event that became the first UFC show ever to surpass 1 million pay-per-view buys.

(Editor’s note: Part 2 (Nos. 15-6 will be next Tuesday) and Part 3 (5-1) will be next Thursday.)