It's not just the four gold medals. Or the enduring emotion of a partisan Parisian crowd. It's also because Leon Marchand managed to achieve something almost everyone thought impossible, and that he will be remembered as the defining figure of the 2024 Olympics.

Victory in the 200-meter butterfly then 200-meter breaststroke on the same Wednesday evening was a feat even his coach, Bob Bowman, thought beyond the limits.

"My coach didn't really want me to do that because it was impossible to do and had never been done before," Marchand told DW. "It was really big chance for me and I was really excited to do it, but I didn't know if it was possible."

It was a surprise even to the most decorated Olympian of all time, Michael Phelps, who was also coached by Bowman. Phelps described it as "probably the greatest double I've ever seen in the history of the sport."

Phelps some way off, for now

Marchand's prowess in the pool have led to comparisons with the American great, who won 23 Olympic gold medals in his career. At 22, Marchand has time to catch up, but without a relay team as strong as the United States one of Phelps' era, it's a tough ask. Nevertheless, the Toulouse native is flattered to be mentioned in the same breath.

"So proud to hear that, honestly," he said. "When people compare me to Mark Spitz or Michael, those guys are legends. They changed the sport forever. I'm not comparing myself to them, I think they were way above, and everything they've done is amazing."

The sports-watching population of France may not agree that the two American greats are "way above" their new idol. But Marchand is only now beginning to realize the impact he has had on his homeland.

"I feel like it changed Paris for a week, it's been magic here. It's been successful. The Olympics have been amazing. Everyone has been watching sport and that's really rare and special for us athletes."

That mutual affection was never more apparent than in that breaststroke win, the second leg of that "impossible" double when the home crowd chanted 'Allez!' (Go!), every time Marchand emerged from the water to take a breath.

"It was kind of shocking at first to have 15,000 people cheering for me," he said. "I had goose bumps over my entire body and I was really using that energy to swim as fast as possible. Every time I took a breath in breaststroke, it was kind of crazy."

US move brings confidence

Marchand may have to get used to life becoming a little crazy, with such a spectacular breakout Games certain to lead to an enormous change in his profile and an increase in temptations. But the Frenchman is mostly just interested in reaching the outer edges of his talent.

"I don't know how fast I can go, or where my limits are," he said. "That's why I train as hard as possible every day to get there. The thing about swimming is that it is about the time. We never know what we're going to reach and I'm just so excited and curious about it."

In an effort to test those limits, Marchand has spent the last three years living and training in the US, following the path of his parents, who were also Olympic swimmers. He is unsure whether he could have achieved what he has by staying in France but says moving stateside has undoubtedly had a significant positive impact.

"I'm really grateful for what the US brought," Marchand said. "I gained a lot of confidence. People there can talk about their ambitions. They are not scared of failing."

Neither, it seems, is Marchand.

Leon Marchand was speaking at a media event hosted by Omega.

Edited by: James Thorogood