One of the most surprising gold medallists so far must be teenage swimmer Ahmed Hafnaoui who won the men's 400m freestyle on Sunday.
The 18-year-old Tunisian won from the outside lane after qualifying slowest, but finished with stunning pace to beat Australia's Jack McLoughlin with a time of three minutes 43.36 seconds. US swimmer Kieran Smith took bronze at the Tokyo Aquatics Centre.
"I just can't believe it. It's a dream and it became true. It was great, it was my best race ever," said Hafnaoui. It was only Tunisia's fifth ever gold - and third in swimming.
Hafnaoui, son of former Tunisian national basketball player Mohamed Hafnaoui, competed in the 2018 Youth Olympic Games, finishing eighth in the 400m and seventh in the 800m.
In 2019, he gave an interview in Tunisia and said he was aiming to win his first gold medal at the 2024 Olympic Games in Paris. Hafnaoui has another shot at gold, in the 800m freestyle.