Fifteen years ago, BJ Penn was a prodigy of nothing. That Penn is now a professional athlete — let alone a world champion — is as stunning as one of his submission moves in an UFC Octagon.

"I remember when I was a little kid, I could run pretty fast," said Penn, 30. "But I never cared about sports, really. If you would have told me when I was a kid that I would grow up and be considered one of the top athletes from Hawai'i, I would have laughed. I'm amazed myself at where I am today."

Today, Penn is the world champion in the lightweight division of the Ultimate Fighting Championship, which is the most prestigious organization in the sport of mixed martial arts.

In effect, he is one of the most popular and influential figures in what is often described as the world's fastest growing sport.

But unlike most other star athletes, Penn does not have a closet full of trophies from youth sports. He played a few years of soccer while growing up in Hilo, but never even tried any other sports.

"We certainly weren't going to force him to play sports," said his father, Jay Dee Penn. "So to think that he's now a world champion ... yeah, I guess it is a little surprising."

At the same time, this is the same BJ Penn who has been viewed more than 3.1 million times on www.YouTube.com for his you-have-to-see-it-to-believe-it physical antics.

In one video, he is standing in a pool, three feet deep, and then jumps out of the water onto the deck without the use of his hands. In another video, he demonstrates how he can place his ankle behind his head simply by stretching his leg up — again, without the use of his hands.

"It's funny how popular those things are," Penn said. "It's just things I found out I could do playing around with friends."

ROOTS IN JIU-JITSU

It is that type of "playing around" that got Penn involved with martial arts in the first place.

"There's times in life to make decisions, and when BJ was about 17, I told him you need to do something else other than just hanging out with your friends," his father said.

Penn chose jiu-jitsu.

"Better than work, right?" Penn said with a laugh.

Penn started taking jiu-jitsu classes at age 17, and over a three-year span, learned from some of the best. He even spent two years in California training under Ralph Gracie. The Gracies are considered the biggest name in Brazilian jiu-jitsu.

By age 20, Penn was a black belt. In 2000, when he was 21, he became the first American competitor to win a gold medal in the black belt division at the Brazilian jiu-jitsu world championships.

Those world titles are normally reserved for Brazilians who start training in the sport at age 4 or 5.

"You really have to win it outright if you're an American; they definitely don't make it easy," Penn said. "As more time goes by, it seems like a greater accomplishment. Definitely one of the highlights of my life."

ON TO THE UFC

A year later, the UFC called, and it's a good thing Jay Dee Penn did not answer.

"When he told me he was thinking about fighting in the UFC, I said absolutely not," his father said. "I was in a real dilemma as a parent. I knew he was technically proficient, but I told him you're going to get hit and that's going to affect you later in life."

BJ, with added support from his brothers, eventually convinced "Pop" to let him take the UFC's offer.

Penn made his UFC debut in May 2001 in spectacular fashion. He defeated Joey Gilbert via first-round TKO.

"That's probably my most memorable fight," said Penn, who has a professional record of 13-5-1. "It was my first time in a big show, and the start is always important — that first impression."

Penn's rise to UFC stardom mirrored his accelerated jiu-jitsu pace. He won his first three UFC bouts via first-round knockout.

He was aptly nicknamed "The Prodigy."

A MERCURIAL CAREER

By January 2004, Penn became a UFC world champion when he upset Matt Hughes for the welterweight title.

Shortly after that fight, Penn got into a contract dispute with the UFC, and left the organization to pursue bouts in Japan and Hawai'i.

"I wouldn't say it was good or bad, it was just something that happened," Penn said. "It was a fun time because I got to sign some fights that I couldn't have had if I was in the UFC."

During his hiatus from the UFC, Penn earned victories over two Gracies — Rodrigo and Renzo.

He also suffered a decision loss to Lyoto Machida of Brazil in a rare open weight bout. Machida, who is now the UFC's light heavyweight champion, out-weighed Penn by more than 30 pounds during their bout.

"I was enjoying the sport, seeing how far I could push myself," Penn said.

Penn came back to the UFC in March 2006, and won the lightweight world title in January 2008.

He is one of only two fighters in UFC history to win world titles in two different weight classes (UFC Hall of Fame member Randy Couture is the other).

Penn's popularity crested in January of this year, when he fought Canada's Georges St-Pierre in one of the most-hyped bouts in UFC history.

Thousands of Hawai'i residents made the trip to Las Vegas to attend the bout, and thousands more watched it on pay-per-view.

"All the support we got for that fight was incredible," said his mother, Lorraine Shin. "It was heartwarming to see so many people backing him."

St-Pierre defeated Penn via fourth-round TKO.

"Of course, he was disappointed, and he needed some time off," his mother said. "But he's back. He's training harder than ever."

Penn will defend his UFC lightweight championship today against Boston's Kenny Florian.

BIG ON THE BIG ISLAND

Penn is the Big Island's biggest celebrity.

"He's huge," said Shane Nelson, a fellow UFC competitor from Hilo. "Everybody and their mom knows BJ. He's bigger than the mayor. We walk into Wal-Mart and there's 60-year-old people down to 5-year-old kids going 'Hey, that's BJ Penn.' "

Scott Murray, owner of the Hilo Fight Company store, said Penn is responsible for the extreme popularity of MMA on the Big Island.

"If Tiger Woods was born and raised in Hilo, I guarantee there would be a ton of golfers here," Murray said. "BJ Penn has created that kind of interest in the sport. People here identify with him. He's one of us, and he made it. Now there's a lot of other kids who want to chase that dream."

Penn and his trainers often jog through Hilo, and Murray said the adulation is evident.

"You hear people yelling 'What's up braddah BJ,' " Murray said. "It's one of those things, everybody wants to feel like they know him. And he feeds it because he's so humble about it. He'll say 'what's up' back to you, or give you a shaka."

When Penn's bouts are televised on pay-per-view, Murray said downtown Hilo "is like a ghost town," because the people are at house parties watching the fight.

He said his store will close early today because Penn is fighting this afternoon.

"I guess I've been fighting on TV a long time now, so it's kind of normal for people to come up and recognize me," Penn said. "I enjoy meeting new people, the fans, and all that. But Hilo is the place that treats me exactly the same as always. That's why it's always going to be home for me."

A GROWING WEB SITE

Want to know what BJ Penn is up to these days? Or every day?

Log on to www.bjpenn.com.

Penn's official Web site has more than 92,000 registered members from around the world. Thousands more view the site daily as non-registered members.

"It started out small, just a way for the fans to keep up," Penn said. "We're a lot more involved now. We try to do as many updates as we can."

Penn's latest success is a video blog that is updated several times a day. It is where the pool jump and leg-behind-the-head videos originated.

When he's not answering questions in front of the camera, he's shooting video from behind the camera.

"I don't really do that much, just take some video with my phone," he said. "My brother (Web master Reagan Penn) does the rest."

The videos give fans exclusive behind-the-scenes views. Just in the past two weeks, there were videos of Penn interacting with Philadelphia Phillies outfielder and Maui native Shane Victorino, and fellow MMA world champions Anderson Silva and Fedor Emelianenko.

What's after MMA?

If Penn were to retire from MMA today, his popularity in Hilo would keep him in business for many more years.The Penn Training and Fitness Center in Hilo has emerged as the town's most popular workout gym, and not just for jiu-jitsu and MMA. The Penn gym also includes a full weight room, various cardio machines, and group fitness classes for men, women and children.

"That's said and done," Murray said. "He got MMA rolling here, and it's not going to stop for a while."

Earlier this year, the UFC announced that it will open a gym in Hawai'i under Penn's name.

"Some days, I think I want to keep fighting for 10 more years," Penn said. "Other days I feel like I'm ready for it to be over. It's a constant push and pull."

Regardless of how much longer he stays in the sport, Penn said he is grateful for the opportunity.

"Everything just fell in the right place at the right time," he said. "Sometimes I think where would I be, what I might be doing, if my dad didn't push me into martial arts in the first place. I have no idea. I was lucky enough to find something I loved and something I was good at, and I want to enjoy every minute of it."