B.J. Penn is one of just two men to win UFC titles in two different weight classes. He has the most wins in UFC lightweight history and owns victories over some of the biggest names to ever step into the Octagon.

Next week, Penn will be inducted into the UFC Hall of Fame before UFC 189 in Las Vegas. But the legendary fighter actually doesn't think the best moment of his illustrious career came inside an MMA cage.

"My greatest moment in my whole career is when I became the first non-Brazilian to win the Brazilian jiu-jitsu world championship," Penn told Ariel Helwani on Monday's edition of The MMA Hour. "That was my greatest moment."

Penn, now 36, won the World Brazilian Jiu Jitsu Championships in 2000, a mere three years after he started training in the martial art. He dispatched Alexandre Soca, Fredson Alves and Edson Diniz en route to the gold medal.

The Hawaiian earned both his brown belt and black belt training at Nova Uniao in Rio de Janeiro under coach Andre Pederneiras. The short time in which Penn earned his black belt earned him the nickname "The Prodigy" in MMA.

"That started it all," Penn said of winning worlds. "When you look back at judo, it was like the first guy who won in Japan that wasn't Japanese. As time goes on, it means more and more to me."

Penn made the transition to MMA soon after in 2001, winning his first three UFC fights via violent knockouts despite his jiu-jitsu pedigree. Penn (16-10-2) would go on to earn wins over Matt Hughes (twice), Jens Pulver, Renzo Gracie, Diego Sanchez, Kenny Florian, Matt Serra and Takanori Gomi. He won the UFC title at both lightweight and welterweight.

The MMA pioneer said if he had any regrets, they'd be "too few to mention." Penn did finish his career with three straight losses. He announced his retirement after falling to Frankie Edgar at The Ultimate Fighter 19 Finale in July 2014. He also took defeats against Nick Diaz and Rory MacDonald at welterweight, so it wasn't as if he was facing slouches.

Penn said he has been tempted by a potential comeback, but has no desire to go back into a training camp. Never say never, he said, but it didn't seem like the return of "Baby Jay" was on the horizon. And, really, he really doesn't have anything left to prove anyway.

"As life goes on, life just gets harder," Penn said. "That's the mark of a man, just keeping your head up, right? Not taking the easy way out."