UFC heavyweight champion Jon Jones announced his retirement Saturday, ending one of the greatest runs in mixed martial arts history.

"This decision comes after a lot of reflection, and I want to take a moment to express my deepest gratitude for the journey I've experienced over the years," Jones said on X.

He continued: "From the first time I stepped into the Octagon, my goal was to push the boundaries of what was possible in this sport. Becoming the youngest UFC champion in history, defending my title against some of the best fighters in the world, and sharing unforgettable moments with fans across the globe - these are memories I'll cherish forever. I've faced incredible highs and some tough lows, but every challenge has taught me something valuable and made me stronger, both as a fighter and as a person."

UFC CEO Dana White initially revealed Jones' retirement earlier Saturday, adding that interim heavyweight champ Tom Aspinall was promoted to undisputed champion.

"Jon Jones called us last night and retired," White told reporters in Baku, Azerbaijan. "Jon Jones is officially retired. Tom Aspinall is the heavyweight champion of the UFC."

Jones added in his retirement announcement that he's "excited" to see how he can still contribute to MMA and inspire others, saying "the best is yet to come."

Jones, 37, stepped into the Octagon for the final time at UFC 309 last November. He defeated Stipe Miocic via third-round TKO at Madison Square Garden in New York, earning his first heavyweight title defense.

In the seven months since that bout, the UFC worked on booking a highly anticipated matchup between Jones and Aspinall. White said earlier this year he was confident it would come to fruition sometime in 2025, but Jones repeatedly downplayed Aspinall as an opponent and said he wasn't interested in fighting him. Jones hinted at retirement several times in the last few weeks.

"Do I regret the time that I gave him (to make his retirement decision)? Listen, if you look at what he's accomplished in the sport, no," White said. "It is what it is. I obviously feel bad for Tom that he lost all that time and obviously money, but we'll make it up to him.

"Tom Aspinall is a good guy. He's been incredible through this whole process that we've gone through. He's been willing to do anything, fight (Jones) anywhere at any time, and now he's like, 'I'll fight anybody. You tell me who, and I'll fight him.' Tom Aspinall has been great. He's gonna be a great heavyweight champion for us. I'm excited to work with him."

Aspinall, who had held the interim heavyweight title since November 2023, reacted to Jones' retirement on Instagram.

"It's time to get this heavyweight division going," Aspinall wrote. "An active undisputed champion."

Jones is widely considered one of the greatest fighters of all time. He's a former two-time light heavyweight champion, former interim light heavyweight champion, and now a former heavyweight champion. Jones holds numerous UFC records, including the most wins in title fights (16) and most successful title defenses (12). He's one of nine fighters to win UFC championships in multiple divisions.

Jones began his MMA career in April 2008 and made his Octagon debut four months later. In 2011, Jones became the youngest champion in promotion history, finishing Mauricio "Shogun" Rua to claim the light heavyweight title at age 23.

Jones defended the 205-pound belt 11 times across two reigns, beating the likes of Daniel Cormier, Rashad Evans, Vitor Belfort, Glover Teixeira, Alexander Gustafsson, Lyoto Machida, and Quinton "Rampage" Jackson. In 2023, Jones moved up to heavyweight and captured the vacant title, submitting Ciryl Gane at UFC 285.

Jones, born in Rochester, New York, but based in Albuquerque, New Mexico, ends his career on a 20-fight unbeaten streak and with a 28-1 (1 NC) record. His only loss was a controversial disqualification due to illegal elbows against Matt Hamill in 2009.

Several legal issues impacted Jones' career. Most notably, Jones was charged with a felony hit-and-run in 2015 after fleeing the scene of an accident that injured a pregnant woman.

Jones tested positive for performance-enhancing drugs twice in his career, in 2016 and again in 2017. He long maintained that tainted supplements led to the failures.