Born in Myanmar, raised by Christian teachers in Thailand, and now trapped in a flooded cave for 13 days, Adul Sam-on's unflinching politeness and startling ability to speak English is capturing hearts.

Images of the wide-eyed teen were beamed around the world when he was discovered alive with the rest of his young football team deep inside the Tham Luang cave.

READ MORE Thai cave rescue: Navy diver dies as weather starts to turn

He remains stuck in the bowels of the mountain as rescuers work out how to get the 12 boys and their coach out safely, a race against time with heavy rains expected to return soon.

"I'm Adul, I'm in good health," the rake-thin 14-year-old said in Thai in a video that emerged hours after the group was discovered, offering a traditional Thai "wai" greeting - trademark politeness, his teachers say.

"The first thing that comes to mind when I talk about him is his nice manner. He gives a 'wai' gesture to every teacher he walks past, every time," his instructor Phannee Tiyaprom at Ban Pa Moead School told AFP.

Adul is also being praised for his English skills in a country where less than a third of the population speaks the language.

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He was the only one able to communicate with the British divers that discovered the boys on Monday night.

"What day is it?" he shouted, telling the divers they were hungry, in footage broadcast around the world after the agonising search for the boys.

Born in Myanmar's self-governing Wa State, young Adul - who also speaks Thai, Burmese, and Chinese - has been at the school since he was seven years old.

He left his family behind to get a better education in northern Thailand, but his parents still visit him at the Christian Church where he's been taken in.

Wa State, a self-ruled region not recognised internationally - nor by Myanmar - is not allowed to legally issue passports.

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Fighting between ethnic rebels from United Wa State Army and Myanmar troops have historically driven thousands from the state seeking safety and greener pastures, including to nearby Thailand.

Adul is among more than 400,000 people who are registered as stateless in Thailand, according to the UN Refugee Agency (UNHCR) - though some estimates put their numbers at 3.5 million.

READ MORE Longing to belong: What it means to be stateless

"Whilst some progress has been made, stateless people in Thailand continue to face challenges accessing their basic rights," UNHCR spokeswoman Hannah Macdonald told AFP.

With no birth certificate, no ID card and no passport, Adul cannot legally marry, get a job or bank account, travel, own property or vote.

Thailand has vowed to register all stateless people by 2024, but until then people like him remain stuck in legal limbo.

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But he refuses to let his status hold him back.

The passionate footballer also loves to play the piano and guitar, and is an accomplished student too.

"He's a gem," school director Phunawhit Thepsurin told AFP.

"He's good at both studying and sports... he's brought our school several medals and certificates from his achievements."