Khabib Nurmagomedov extended his perfect professional record as he retained his lightweight title at UFC 254 in Abu Dhabi - then announced his retirement.
Russian Nurmagomedov, 32, defeated interim champion Justin Gaethje with a second-round triangle choke submission to claim a 29th victory and unify the 155lb title.
Nurmagomedov said he had honoured the memory of his father, coach and mentor Abdulmanap, who died in July following complications arising from Covid-19.
Despite many believing Nurmagomedov would chase his 30th professional win before contemplating retirement, the emotional champion asked his team-mates to cut his gloves off before quitting.
"It was my last fight. There's no way I'm going to come here without my father," he said. "It was the first time after what happened with my father, when the UFC called me about (fighting) Justin, I talked with my mother for three days.
"She didn't want me to fight without father, but I promised her it was going to be my last fight, and if I give my word, I have to follow this. It was my last fight here.
"I know only one thing I want from the UFC: Tuesday, you guys have to put me number one pound-for-pound fighter in the world because I deserve this.
"Undisputed UFC lightweight champion, 13-0, 13 in the UFC, 29 in my pro MMA career. I think I deserve this."
Nurmagomedov 'broke his foot three weeks ago'
"What this guy's been through, we're all lucky we got to see him fight tonight," said UFC president Dana White. "I'm hearing rumours of other things that I didn't know about. Apparently he was in the hospital. He broke his foot three weeks ago. So he has two broken toes and a bone in his foot that's broken - that's what his corner was telling me. Never told anybody.
"He is one of the toughest human beings on the planet and he's the number-one pound-for-pound fighter in the world and, seriously, you have to start putting him up there with GOAT status with whoever else you think is the GOAT."
UFC 254, which marked the final event of the sport's second stint on Yas Island, saw the return of Nurmagomedov, who was unable to defend his title earlier this year because of Covid-19 travel restrictions in Russia.
At the time, Nurmagomedov was due to face rival Tony Ferguson at UFC 249, but Ferguson instead faced Gaethje, and was stopped in the fifth round as 'The Highlight' claimed the interim title and stepped into the number-one contender spot.
Gaethje was expected to pose problems for Nurmagomedov, with his collegiate wrestling experience considered a possible antidote to the champion's smothering grappling style.
But Nurmagomedov dominated the first round with his high-pressure approach, then submitted Gaethje in the second.
Nurmagomedov added Gaethje's name to a list of beaten opponents that also includes Dustin Poirier, Conor McGregor, Al Iaquinta and Edson Barboza.
Nurmagomedov thanked Gaethje, who had arranged for his parents to fly internationally for the first time in their lives to watch him fight for the title, and paid tribute to a man who four years ago helped him make weight when he was struggling to lose the final few pounds for his short-notice fight with Darrell Horcher.
"Thank you so much, Justin. 2016 I remember when I cut weight, you helped me a lot. Thank you, brother," Nurmagomedov said.
"I know how you are a great man. I know how you take care of your close people. I know a lot of things about you.
"Be close with your people, because you never know what's going to happen tomorrow. You never know."
Whittaker wins again while Wood nets $50,000 bonus
In the night's co-main event, Australian former UFC middleweight champion Robert Whittaker continued his return to form since losing his title to Israel Adesanya last October by outpointing American Jared Cannonier to move back into title contention at 185 pounds.
British bantamweight Nathaniel Wood was also in action, but was edged out on the scorecards after a back-and-forth battle with American Casey Kenney on the preliminary card. However, their 140-pound catchweight match-up was awarded "Fight of the Night" honours, with both men receiving $50,000 bonuses for their respective performances.