A fierce competitor and blessed with natural talent, Vaast seemed born to tame the waves -- his name means "the one who goes in the ocean" in Hawaiian.
"Teahupo'o is his garden," said Pascal Luciani, former president of the Tahiti Surfing Federation.
Vaast, 22, seemed destined for surfing glory from a young age. He first stood on a surfboard aged four with his father and won his first junior title in Tahiti at the age of eight.
"From that day on I knew that I wanted to surf all the time and to this day I haven't stopped," he said.
After growing up in Mahina, in the north of Tahiti, he moved with his parents to the village of Teahupo'o to face some of the world's most dangerous waves.
"Kauli is not scared of the wave but many others fear Teahupo'o," said Vaast's Olympic coach Hira Teriinatoofa.
Even when he was not surfing the rolling waves, he was in the ocean, diving or fishing "pupuhi"-style with a harpoon gun in the turquoise waters.
Vaast could dive for fish 20 metres below the surface, revealed childhood friend Mauri Ebb.
"We fished, we surfed, we ran together. Even when we were jogging, he would go much faster than anyone else. He would wait for me and I would struggle on behind," said Ebb.
'Washing machine'
The competitive spirit that would take him to France's first Olympic surfing gold was evident from a very young age.
"He always had to be first, even to get through the door, to the car, or to the fridge," recalled his mother.
Olympic coach Teriinatoofa said: "He likes to dance and horse around outside competitions, but he does everything he can to win."
As a teenager, he won local judo tournaments and school cross-country runs but then the surfing titles began to pile up -- European junior champion in 2017, 2019 and 2020.
In 2021, he took on a wave estimated at 15 metres high at Teahupo'o. "His wetsuit was partly ripped off" by shards of coral smashed up by the wave, said his mother.
"He went through the washing machine."
Former pro surfer Raimana Van Bastolaer, known as the "boss" of Teahupo'o, has been instrumental in Vaast's journey to Olympic gold.
"He's taken care of me since I was young, he's always been there. Helped me find sponsors, looked after me at Teahupo'o, basically been a second father," said Vaast.
Van Bastolaer said his protege had to grow up quickly -- even at the age of 11 he was travelling solo to train with other surfers in Hawaii for months at a time.
"He's very mature. He can surf big waves or small, do the 'aerials', all the moves. He's very strategic," said Vaast's mentor.
'The mana was with me'
Even with an Olympic gold medal around his neck, the local prodigy did not forget his roots.
"The mana was with me today," Vaast said after the win, referring to a supernatural force in Polynesian culture.
"From the beginning, every day I felt it, it was there."
And the conveyor belt of family talent does not stop with Vaast.
His younger sister, 19-year-old Aelan, has already enjoyed success in her own right, taking inspiration from the "super powerful, fluent" technique of her older brother.
Vaast's younger brother Naiki is already making a name for himself in the Teahupo'o waves at the age of 16.
But for Kauli Vaast, Olympic gold seemed written in the stars as soon as the surfing competition for the Paris Games was located at home, nearly 16,000 kilometres (9,950 miles) from the French capital.
Winning on his home turf of Teahupo'o was "the cherry on the cake", he said. "For all of France, for all of Polynesia it's incredible."
