PARIS—There has never been anyone better at flinging himself astonishingly high in the air with the help of nothing more than a bendy pole than Mondo Duplantis.

The greatest pole-vaulter of all time entered Monday as the reigning Olympic champion and was a lock to win another gold from the moment he landed in France. Duplantis had single-handedly lifted the world record from 6.17 meters to 6.24. And the only thing more remarkable than how much he’d raised the bar was how many times he’d done it.

Duplantis jumps higher than any human who has ever walked the earth. A lot higher. So much higher, in fact, that his only serious rivals are himself and the earth’s gravitational pull.

“He’s like the Usain Bolt of pole vault,” says American pole vaulter Chris Nilsen.

Forget about trying to beat him. Duplantis floats nearly a whole foot higher than any of his opponents. So the question as he won his second consecutive Olympic gold on Monday wasn’t  whether he would do it. It was whether he would do something that nobody had ever done before—for the eighth time.

“People just want to see a world record,” he said in an interview before the Games. “People don’t care at all how much higher it is. Every time I step on the track, that’s the only thing people want.”

At the Stade de France on Monday night, Duplantis gave them absolutely everything they wanted.

After he took care of business and comfortably secured the gold medal, he signaled that he wanted the bar raised to 6.25 meters. On his first attempt, he grazed the bar. On his second, he kicked it again. He ran over to the crowd to review footage on a tablet with his parents. Then, with all other action frozen inside the stadium and the crowd egging him on with chants of “ Allez   Mondo !” he closed his eyes, took a deep breath and prepared to fly.

Moments later, Duplantis made sure that he left the Paris Games with another gold medal, a pristine Olympic moment and what he really came for: the new world record.

Even a team with LeBron James and Stephen Curry wasn’t nearly as much of a sure thing to win gold as a 24-year-old Swedish guy who launches himself over two basketball hoops with a few inches to spare.

If you bet $10 before the Olympics on Team USA winning gold in men’s basketball, the reward would be $2.13. Duplantis was such an overwhelming favorite that the same $10 bet on him paid out 29 cents.

But there’s one person who does stand to make a killing whenever Mondo Duplantis wins and sets a new world record. His name is Mondo Duplantis.

That’s because major track meets offer bonuses to athletes if they break a world record. In other words, Duplantis has a powerful incentive to keep bumping the bar to unprecedented altitude—but only by a single centimeter each time. The man who can climb more than 20 feet high is always trying to catapult himself just 0.4 inches higher.

At a pre-Olympic meet last month, Duplantis attempted to break his record and just barely missed. It cost him $50,000.

But on Monday, when he did manage to clear the bar at 6.25 and Abba reverberated around the Stade de France, it made no sense for him to shoot for 6.26. In fact, it would have been a terrible financial decision. The more often he breaks his own record, the more he gets paid.

Duplantis doesn’t rewrite history for free. He thinks about that bonus every time he challenges the boundaries of human flight.

“I’d be lying if I said it didn’t,” he said.

He’s able to improve by precisely one-centimeter increments because unlike the long jump, which measures the exact length of each jump, the pole vault’s world record is simply a matter of how high Duplantis sets the bar. If he boosts it to 6.26 meters and clears it by a few centimeters, the world record is still 6.26 meters.

In training, he jumps about 20 centimeters lower, which means not even he knows what to expect at meets. Sometimes, he soars over the bar with daylight to spare. “And sometimes,” he says, “I couldn’t go a quarter of a centimeter higher.”

The son of an American pole-vaulter and Swedish heptathlete, Duplantis is a dual citizen who grew up in Lafayette, La. For most of his life, the world record in the pole vault belonged to Olympic legend Sergey Bubka, who pushed it from 5.85 meters to a previously unthinkable 6.14 meters between 1984 and 1994.

That’s where it would remain for the next 20 years.

French pole vaulter Renaud Lavillenie hit 6.15 meters in 2014, and it took until 2020 for Duplantis to pass him by one centimeter. But it didn’t take long for Duplantis to beat himself. One week later, he broke the world record again.

Since then, he’s done it so many times that even Lavillenie doesn’t compare himself to Duplantis these days.

“He’s clearly on another planet,” he said.

Perhaps more than anyone on this planet, Lavillenie understands exactly what it takes every time Duplantis indicates he’s ready to go higher. He was in the crowd on Monday night, when Duplantis made sure the real action started when the competition was already over.

Write to Joshua Robinson at Joshua.Robinson@wsj.com and Ben Cohen at ben.cohen@wsj.com