Athletics: Olympic 100m gold medallist Justin Gatlin knows his rivals are snapping at his heels

As the shutters whirred for Justin Gatlin, the 23-year-old who surprised nearly everyone except himself by taking the blue riband gold in the Athens Games last summer, the man from whom he inherited that title, Maurice Greene, was slipping quietly into a courtesy car. As his driver moved off, the man who has dominated the 100m event in recent years - unable to run in today's Norwich Union London Grand Prix because of an injury - stared balefully out of the window at the young man now being fêted.

A year earlier, Greene had been the star turn in the same room where Gatlin had just given a press conference. The man who won three successive world championships and set a world record presented the familiar, brash persona exemplified by the latest addition to his tattoos - G.O.A.T, standing for "Greatest Of All Time".

There is no such showboating from Gatlin, whose bright and lively face has more than a hint of the Prince of Bel Air himself, Will Smith. When he smiles, his teeth shine as brightly as the diamond in his left ear. He smiles a lot. And he has a lot to smile about. The Olympic final last year was seen as a rivalry between the belligerent defending champion and the 22-year-old Jamaican who beat him decisively in the pre-Games meeting at Crystal Palace last year, Asafa Powell. But both were surprised by Gatlin, who became the youngest Olympic 100m champion since Jim Hines in 1968. He went on to take silver in the relay and bronze in the 200m.

A year earlier, Gatlin had emerged to international recognition by beating Mark Lewis-Francis to win the world indoor title in Birmingham.

He has been fortunate, as well as successful, in his career so far. At 19 he received a two-year ban for doping when amphetamines were discovered in a sample, but the international authorities pardoned him within two months because the test result had been caused by medication he was taking for attention deficit disorder.

Clearly he is not overly sensitive to the issue, as his coach is now Trevor Graham, the former guru to Marion Jones, who has admitted that he sparked off the investigation into the Balco lab which threatens to bring down both Jones and her partner, the former world record holder Tim Montgomery, by sending the US anti-doping authorities a sample of the new designer drug THG anonymously.

Gatlin is open about the question of doping, and accepts that people are wary of outstanding performers in his events given the bad publicity generated by the Balco scandal. "There is a cloud, but we can take that cloud away," he said. "I know what to say no to and what to say yes to. If any allegations come up, I know it doesn't involve me."

Fortune also favoured Gatlin at the US trials last month in Carson City, where he appeared to be out of the World Championships after false-starting but was restored after a lengthy appeal when it was adjudged he had been reacting to the runner next to him.

So here he is, ready to extend his Olympic success with another impressive performance at the World Championships which start on 4 August in Helsinki, where he will seek both the 100m and 200m titles.

With Greene, who turns 31 tomorrow, looking increasingly on the wane, the question hangs in the air: who will succeed him? Gatlin hopes he will be that athlete but he acknowledges that there are several contenders in what he describes as being more of a young man's event nowadays.

Powell, who lowered the 100m world record to 9.77sec earlier this season, is the obvious rival, albeit that he is still carrying a groin injury as an unwanted legacy of that run.

He feels the rivalry can take the event to a new level. "I think so," he said with a dazzling grin. "Don't you love that? The story behind it? The Olympic champion against the world record holder. And that's what we're trying to do right now - uplift track and field. Of course, we both have respect for each other, but when we go out there we want to annihilate each other, basically. The world record has been ticked down by a notch the last three times. I want to go out there and put another notch on it, make it 9.75."

He accepts that becoming the Olympic champion has changed him. "It turns you into a man," he said. "You have to go out there knowing you have a lot of responsibility to a lot of kids. I have a lot of young athletes in America who call me and tell me about their progress in their track and field meets, and I support them in the same way they support me. And that support system has helped me this year to be more aggressive and to go out and win my races.

"Everyone thought I had a chance to win in Athens but no one thought I would win. That's the thing I love about track and field - it's unpredictable. Even in the 200m there's so much talent around. You have Wallace Spearmon and Tyson Gay of the United States, you have Usain Bolt in Jamaica, you have great talent in Britain."

Gatlin will double up in Helsinki, but he believes the hardest part will not be the running. "It will be preparing for each round - going home on time, being responsible, not hanging out, taking ice baths and getting massages. It's knowing how to prepare myself to be a champion. Being aged 23, it's hard to be disciplined. You want to go and hang out with your friends: a lot of my friends don't run track, they're out socialising, going to clubs, drinking, just being young. But obviously I can't do that right now - I have to go out there and concentrate on my races."

This young man is being carefully monitored by his agent, the former world high hurdles record holder Ronaldo Nehemiah.

"I've told him that when it's time for him to leave the sport, if he's only remembered for how fast he ran I'd be sort of disappointed in him. He has obligations to give back to the sport," Nehemiah said.

"He comes from a middle-class family in Brooklyn - his father has a military background, his mother works in marketing with a New York advertising company. He is a very disciplined and respectful young man, who has been reared with those fundamentals in mind. He allows me to give him direction. He never feels he's bigger than life.

"My whole motivation when I was running, I called it the Wow System. I always wanted to wow people. It was about how much fun I had, taking time out to meet people, to have people cheer for me and have the utmost respect for me because of the way I played the game. That's the same thing I try to impart to all of my clients, including Justin. You're not a one-dimensional person."

Crystal Palace awaits the latest demonstration of Gatlin's special talent.