If the name doesn't ring a bell, and you haven't caught up with this season's SAS Australia yet, think back to 2018, when a young football team were rescued from Tham Luang Nang Non, a cave system in Chiang Rai province, northern Thailand. He and fellow Australian diver, anaesthesiologist Richard Harris, played a vital role in the rescue.

Dr Challen modestly says he was there for only three days of the rescue mission, but they were the most critical days of the extraction.

"I was in the right place at the right time," the humble veterinarian says.

So, why would this Star of Courage, OAM, and 2019 co-Australian of the Year awardee, feel the need to go through the gruelling SAS Australia boot camp?

"Well, it was for the experience I suppose... I'd never done anything like that before," Dr Challen says.

The 57-year-old is the oldest person ever to take part in the franchise, along with 2023 fellow participant actor Craig Mc'Lachlan.

"I've got a few more miles left in me," he says drily.

On taking part in SAS Australia, Dr Challen says he was a little apprehensive.

"I got asked to do it. I'd done at least something like the activities on the show, so I wasn't fazed by any of them. But I'm not a professional athlete and certainly wasn't the strongest or fastest [of the candidates].

"I didn't know many of them, I don't watch TV, so the sports people were the only ones I had really heard of. I wasn't intimidated by them. I've met a lot of well known and famous people, and they all put on their trousers one leg at a time.

"It's mostly a challenge against yourself. I didn't see it as a challenge between people. When you are confronted by these circumstances you rise to the challenge or not.

"I do not try and second guess things like that.

"I've got no experience of the type of tests they [the other recruits] went through. Everybody rises and falls on their own. I don't judge people.

"I have a 100 per cent success rate at things I've tried because I don't put limits on myself."

Dr Challen says he likes to keep healthy, and maintain a level of fitness mostly by running and bike riding.

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Of the 14 celebrities - Abbey Holmes, 32 - AFL field commentator; Anthony Mundine, 47 - World Champion boxer; Boyd Cordner, 30 - retired NRL star; Cassie Sainsbury, 28 - convicted drug smuggler; Dr Craig Challen, 57 - Thai cave rescue hero; Craig McLachlan, 57 - actor; Jason Akermanis, 46 - AFL Hall of Fame; Lindy Klim, 45 - Balinese princess; Mahalia Murphy, 29 - international rugby star; Matthew Mitcham, 35 - Olympic Gold diver; Peter Bol, 29 - Olympic runner; Stephanie Rice, 34 - Olympic champion; Tim Robards, 40 - original The Bachelor; Zima Anderson, 25 - actor; - dropped in the Jordanian desert, only eight remain after the fifth punishing day, either through voluntary withdrawal, or injury.

Will Dr Challen be the last person standing? You will have to watch and see.