He was a Buddhist monk apparently. I've copied this from Canary's link for those who haven't read it.
// Assistant coach Ekapol Chantawong (Nickname: Ake), 25
Ake was reportedly born in Myanmar and lost his parents at a young age.
Prior to becoming a football coach, he spent several years as a Buddhist monk, and learnt how to conserve energy by restricting movements and meditating. According to local news reports, he taught these techniques to the boys in the cave.
In his letter, Ake apologised to the parents for taking the boys into the cave network, but several replied to say they did not blame him.
"I promise I will take care of the kids as best as I can," Ake wrote.
Some media reports suggest when the group was found Ake was weakest, having refused to eat any of the food they had brought with them, giving it instead to the boys. \\