Outside of the water, you’ll mostly find her smiling (or dancing!) with the air of someone that doesn’t take life too seriously.
But in the pool, the Hungarian's relentlessly competitive alter ego the ‘Iron Lady’ comes out.
At the Rio 2016 Olympics, Hosszu stormed to three individual gold medals in the 100m backstroke, and 200m, and 400m medley races.
That, coupled to her nine individual world titles, demonstrates the hunger she has to be the best, and it's more than likely she will be adding to that medal tally at the Tokyo Olympics in 2021.
Let’s explore where that drive and determination come from, and find out more about some of her most memorable moments.
Some swimmers are genetically-blessed with big shoulders, long limbs, and low body fat. That was certainly not the case with Hosszu.
"When I was a girl I used to be pretty chubby and not very tall. In training they (the coaches) believed I didn't belong there, and so I believed it too,” the 31-year-old shared at an Empowering Women in Sport Conference in 2019.
"Believing that I would probably never become an Olympic Champion, I still wanted to swim because that always remained my passion."
The Hungarian persevered with a goal of performing well enough simply to get an education abroad and learn English.
Aged 19, she was awarded a scholarship to the University of Southern California to study psychology, and ended up having one of the greatest college seasons ever in 2011, with three individual national championships titles.
From that point onwards her life was set on a very different course towards Olympic stardom.
While Katinka is the only Olympic champion in her family, she is one of many professional athletes.
Her father Istvan was a basketball player, and her older brothers Gergely and Adam - both inheriting their father’s tall genes at 1.9m (6-foot-3) - followed suit.
As if that wasn’t enough, Adam has also represented the Hungarian national team in futsal.
Imagine how competitive the Hosszu family workout sessions are…
With her steely focus and seemingly endless drive to win gold medals, this must be one of the most apt nicknames in sport.
The origin? China.
After beating Chinese 200m butterfly Olympic champion Jiao Liuyang in 2012, Chinese newspapers used the term ‘Iron Lady’ to describe Hosszu as she never seemed to get tired despite swimming in so many events.
Hosszu liked the theme so much in fact, that she developed a whole swimwear line using the theme!
In an Olympic Channel interview from 2018 below, she explained how the alter ego helps her in competition.
Despite her amazing success in the water, Hosszu is far more than just a swimmer.
In 2016 she wrote a two-part book series inspired by her difficult comeback from the London 2012 Olympics, where she surprisingly failed to medal.
“My main goal of this book is hopefully to change the mindset of at least one person for the better," Hosszu said when it was published.
Off the back of that came the launch of her Iron Nation YouTube channel, where fans can see what life is like for professional swimmers behind the scenes.
And she then added her comic book series 'Iron Lady - Arcanum'.
Coming from a basketball family, it's probably not such a surprise that Hosszu is also a big fan of the sport.
However did you know that her hero in the sport is fellow Olympic gold medallist and NBA superstar LeBron James, and that she once made a sign for him that caught his attention during a Cleveland Cavaliers game?
She later wrote on her Instagram of the moment:
"At the end of the first quarter, after a time-out, he was looking directly at me, and Lebron started to squint to read my sign from far away, then he put his hands together and bowed for me, pointed his index finger at me then started to run because the game continued.
"I think this was an amazing thing he did, he took his time to read my sign and honestly reacted to it during a game while I am a stranger to him, I am just one of more than 10 million of his fans. And this is why he is my hero!"
Given that moment happened before Hosszu became a three-time Olympic champion, we dare expect that she is also now squinting into the crowd to read her fan messages at swimming meets!