Katie Ledecky may seem peerless in the pool but to continue making history she'll have to overcome her greatest rival: herself.
A 5-time Olympic gold medallist, a 14-time world champ, 14 world records broken so far.
All that and she's still only 22.
Now, as Tokyo 2020 is within visibility, the greatest challenge for one of the greatest swimmers of all time is to surpass what she's already achieved.
The question is, can the Katie Ledecky of 2019 and 2020 compete with the Katie Ledecky of 2015, 16, and 17?
The best thing about Team USA's history-making, record-breaking swimmer is that there is no secret.
No hidden lungs behind the ears or webbed feet.
She's not one of the X-Men, or the Avengers, or whatever the latest thing is.
Just an ordinary person capable of extraordinary things.
Ledecky sets clear goals, then finds the way to get there. Relentlessly.
Mid-May 2019 she told an Omaha TV station that:
"I set big goals for myself. Right after Rio I set my new goals for this four year chunk and I'm getting closer to making those goals happen in 2020."
Typically for this low-key luminary, the interview has less than 700 views on YouTube.
But that's her tried and tested formula, small steps that lead to world dominance.
“When I was a kid, I would write them down, and I would work toward them, and that’s still pretty much what I do.”
Eat. Sleep. Swim.
Or maybe not.
'Getting there' takes a superhuman level of commitment and sacrifice: It's swimming 10,000 metres a day, practically every day, six hours in the pool, staying intensely focused on those goals and what it takes to get there.
Then there's the analysis, the coaching, the listening, the improving, the technique tweaks that shave off tenths of seconds.
And somehow finding a way to make all that fun.
“One thing about swimming that people don’t really know, is that the work you put in practice shows off in the meet.” - Katie Ledecky
Her coach Bruce Gemmell tells a story about her as a child that says it all:
It's 2003 and Katie is six years old. Her first ever race is a 25m swim at a local meet - one length of the pool.
Little Ledecky stops a number of times to grab the lane rope to rest and breathe and keep going, before just about finishing the race.
Her dad David captures the moment forever on a video camera, unwittingly conducting the future multi Olympic champion's first ever post-meet presser.
"Tell me about your first race, how was it?" he asks.
"Great," Katie replies with a huge smile, "That was hard!"
Now 16 years later, she's exactly the same: The joy for Ledecky isn't just in the winning, it's in the working for it, earning it.
“Her strength is not in any physical attribute. It’s not even in any particular technique," Gemmell explains to the Washington Post, "it’s her overwhelming desire to do what she needs to do to get better."
Ledecky is constantly on a mission to fail better.
“There are days she fails catastrophically,” Gemmell says, “She fails in practice more than anybody in her group, because she’ll start out like, ‘This is the pace I need to swim in the race, so I need to replicate it in practice.’
"And she’ll go six repeats like that, and the tank goes empty and she just falls off. But you know what? She’ll come back the next day and try it again. And on the third day, she’ll nail it. And she’s been doing this since the first day I walked on the deck with her.”
The Washington D.C. native has conquered long distance because she doesn't swim like a long distance swimmer, her approach is that of a sprinter, exploding off the starter block so fast that she's ahead before she even hits the water.
Most long distance swimmers are pacing themselves so that they're not tired at the end of the race, Ledecky wants to have the race won by the final 10-15 metres.
And she usually does.
Focussing on her own 'race pace' - or her target stroke rate - and rhythm during training has visible results that she maintains on race day.
To stay sharp Ledecky spars in the pool with men, and regularly beats them, it's all part of the process of challenging herself on daily basis.
And the results speak for themselves: sometimes she's so far ahead of her rivals that it looks like she's alone in the pool racing against herself, immersed in her own thoughts.
The prodigy who won her first gold medal at 15 years of age at London 2012 is more aware than anyone of the challenge that a hungry new generation can present to her at Tokyo 2020.
In London the USA upstart ended UK swimmer Rebecca Adlington's dreams of home gold.
At 23 Adlington was the defending Beijing 2008 champion and world record holder, and none of it mattered to a hungry young Ledecky.
Since then the U.S. sensation has become the undisputed queen of long distance and the ruler of all things freestyle, right now Ledecky is:
We're talking about someone who has never lost an 800m race - a life-long unbeaten streak.
At the Kazan world championships in 2015 Ledecky produced a dazzling display of swimming over a range of disciplines that no-one had ever seen before, an unthinkable clean sweep of five events.
So new was it that they gave it her name: The Ledecky Slam.
But no-one stays queen forever.
At Budapest 2017 she finished second in the 200m race and finished with 4 titles, Italy's Federica Pellegrini daring to deny Ledecky a second slam in her own name.
Pellegrini is in the conversation, but who else can live with the USA's phenom?
One name to watch out for is Wang Jianjiahe, who became only the third female swimmer in history to go under 8:15secs in the 800 free by swimming 8:14.64 in the Chinese national championships.
It was the fastest 800 in 2019 until Ledecky swam 8:14.24 at the TYR Pro Swim Series in Richmond in April.
"I'm aware of what everyone else in the world is doing," Ledecky said afterwards.
Australia has a couple of contenders who'll be keen to do to Ledecky in Tokyo what she did to Adlington in London: 18-year-old Ariarne Titmus, and Emma McKeon, 25 who could test USA's dominant one over 200 and 400 metres.
But with the women's 1500m freestyle being introduced at the Japan Olympics in 2020, it means that Ledecky could compete for six gold medals - 4 individual and 2 relays.
There's no doubt that her goal is to win all six.
So what's the hardest thing about being Katie Ledecky?
Beating Katie Ledecky.
"I would encourage you to set really high goals. Set goals that, when you set them, you think they’re impossible. But then every day you can work towards them, and anything is possible, so keep working hard and follow your dreams.” – Katie Ledecky to the New York Times