“I never lost to an opponent. I lost to diverticulitis. That was my opponent that beat me,” Brock Lesnar once said. Although it’s been over a decade since he left mixed martial arts, the sentiment around Lesnar’s invincibility continues to linger. Had it not been for medical reasons, Lesnar’s longtime manager Paul Heyman believes his career as an unbeaten UFC champion would have lasted well into his late 40s.

“If he didn’t have diverticulitis, he would have never been defeated in the UFC,” Heyman told Graham Bensinger. “Never. Never. He’d still be champion today at 49. There’s nobody on this planet that could hang with him, no one. No one. No one. No one would get out of the first round with him. There’s no way.”

Given he has been with Lesnar since 2002, Heyman’s confidence in Lesnar’s skills is understandable. While it lasted a few years, an incredible run saw Lesnar conquer the heavyweight division in the UFC.

He suffered a setback after Frank Mir forced a first-round submission on February 2, 2008, eight months after he made his promotion debut. However, Lesnar rebounded, and on November 15, 2008, captured the heavyweight title by defeating Randy Couture via second-round TKO.

Following two successful title defenses, which included a win over Mir, Lesnar suffered his second MMA defeat when Cain Velasquez stopped him in the first round. A first-round loss to Alistair Overeem subsequently followed.

Meanwhile, Lesnar experienced mounting complications from diverticulitis.

In 2009, after the Mir rematch, Lesnar reportedly collapsed during a hunting trip. The diagnosis revealed severe diverticulitis alongside a weak immune system, forcing Lesnar to pull out of scheduled title defenses against Shane Carwin. After undergoing a diverticulitis surgery in November 2009, Lesnar returned by July 2010 and defeated Carwin via second-round submission.

After the loss to Velasquez, the disease returned, forcing Lesnar to pull out of a fight against Junior Dos Santos. He underwent an emergency surgery in May 2011, with doctors removing 12 inches of his affected colon.

Seven months later, Lesnar returned for the Overeem fight. Reports suggest, knowing Lesnar’s medical condition, the Dutch kickboxer went for his midsection and attacked with a vicious left kick. Lesnar fell onto the canvas before the referee stopped the fight.

The loss seemingly became a catalyst for his first departure from MMA. The severe physical and mental toll of the illness became unbearable. Addressing the crowd at UFC 141, Lesnar revealed that he had told his family he would walk away if he lost.

While he stepped away from MMA, Lesnar remained active and a few months later returned to competing in the WWE. The sport’s controlled environment was much safer when compared to the highly volatile physical nature of cage fighting.

But the lure of MMA glory proved irresistible, and Lesnar returned in 2016 for one last run, facing Mark Hunt at UFC 200. Speaking about his return. Lesnar said, “I couldn’t live with that decision for the rest of my life. I don’t want to be sitting 20 years from now, saying, ‘You know what, son, you should have gone and done that.’ And here I am.”

Beyond his motivation, business reasons likely compelled Lesnar’s return. He was 38 and understood that time was running out. Reportedly, he managed to convince WWE chief Vince McMahon to allow him a crossover opportunity in exchange for massive advertisement for the platform’s upcoming SummerSlam.

The win over Hunt was subsequently overturned after Lesnar tested positive for a banned substance, and he eventually walked away from MMA for good.

Whether Lesnar would have had an unbeaten run, had he continued, remains one of the greatest “what ifs” of MMA.

Brock Lesnar: An unstoppable force, an unbreakable legacy

Aligning with Heyman’s suggestion, the consensus remains that Lesnar would have been unstoppable had he operated at his full capacity. Lesnar himself appears to have admitted that even during his championship run he was fighting at 70% of his physical capacity.

So does that mean he would have been unbeatable? It does not appear so.

Fighters like Velasquez and Overeem, who possessed both striking abilities alongside great wrestling defense, exposed a major flaw in Lesnar’s fighting style—his tendency to shut out when put against a dominant fighter. Even if he had fought at his 100% capacity, overcoming the flaw would have been a daunting challenge.

Besides Heyman, there are many who believe Lesnar would have been dominant for a long time.

Reflecting on a hypothetical fight between Lesnar and Jon Jones, former champion Kamaru Usman felt the WWE star would have been too much for Jones.

“This is an outrageous question…who would win? Hypothetically, I would say the sheer size of Brock Lesnar and the way he wrestled,” Usman said on the Pound 4 Pound podcast. “Brock Lesnar wasn’t necessarily a guy ripping shots all the time, but he could wear guys down… Brock would be a bit more offensive, and trying to get a guy of that size down multiple times? I just don’t see it. I think Brock Lesnar potentially [wins].”