When he was just seven Dej earned a paltry $2 for his impoverished family every time he got into the ring as a child Muay Thai boxer.
Thirty years on, he pulls in a six figure salary as a mixed martial arts champion and is preparing a title defence in Thailand, a country with a proud kickboxing heritage that is wary of modern cage fighting.
Thailand's famous Muay Thai has long provided a route out of poverty for some of the country's poorest kids, who are drilled for the brutal contact sport from a young age.
Most never make it big. But for those who do, fame and comparative fortune await, even if the physical costs are often high.
Now the growing international clout of MMA is offering an even greater lure to Muay Thai fighters -- and that has ruffled the feathers of traditionalists in Thailand who fear the all-action sport may one day eclipse the kingdom's venerated boxing style.
"I haven't fought in Thailand for years," Dej, who is now based in Singapore and whose full name is Dejdamrong Sor Amnuaysirichoke, told AFP during a recent visit to a Bangkok gym.
"But I'm still a Muay Thai fighter at heart so I'm delighted to be doing it here."
In recent decades MMA has gone from a niche sideshow to a multi-billion dollar industry and one of the world's fastest growing sports, with Asia no exception.
Many cage fighters are trained in Muay Thai, a technique that uses fists, elbows, knees and kicks and offers versatility to an MMA fighter's arsenal.
But the international MMA fight circuit noticeably missed Thailand, primarily because the country's sports authorities and Muay Thai leagues had been loathe to allow a competitor in.
Now that is set to change.
On May 27, ONE Championship, by far Asia's largest MMA organiser, will put on a fight night at a 10,000-seat arena in Bangkok, the first time a major promoter has been allowed to hold such an event in Thailand.
For Dej, a three-times Muay Thai champion who switched to MMA late in his career notching up six wins and no losses, it is a homecoming.
At the fight, he will be defending his strawweight title against Japan's Yoshitaka Naito, a 32-year-old Shooto trained fighter who is also undefeated with 10 victories to his name.
"It's an opportunity to show Thailand that mixed martial arts fighting is a sport. And it's also a way to show Muay Thai on a bigger international stage," he said.
MMA, with its far larger global audience and sponsors, offers even greater riches. As a ONE insider put it: "The top guys like Dej, they easily pull in six figures in US dollars" annually.
By contrast, the average Muay Thai pugilist can expect little more than $100 for a fight, with the headline bouts perhaps upwards of $5,000.
Both sports offer rewards far in excess of the $5 a day offered for menial jobs or farm work -- the traditional route for many poor young men in Thailand -- making them an attractive alternative to the disenfranchised.
Born into a poor family in southern Trang province, Dej began training in secret because his mother was so opposed to him taking up Muay Thai.
But he excelled and moved to Bangkok as a teenager, eventually competing in more than 300 fights.
He recently visited his old master Prawit Teryou, who has trained generations of young fighters, usually from poor backgrounds, from his house in a non-descript residential suburb that boasts a boxing ring in the front garden.
"About 20 of us used to sleep here," Dej told AFP, pointing to a small room at the back of Prawit's compound. "It was a boxer's life, a big family's life."
"Muay Thai is definitely still a way for them to help their family," explained Prawit, a wizened and mustachioed trainer with a Buddhist amulet hanging from his neck.
But Dej's sporting and financial success has piqued local interest in MMA.
"There's certainly a lot of interest in mixed martial arts from kids in the gym now," he said, adding he doesn't understand traditionalist opposition. "In the end MMA is a sport, like Muay Thai is."
The Sports Authority of Thailand wants cage fighting banned in the kingdom, saying it threatens Thai culture and is overly violent -- something which has raised wry smiles among fight promoters who say Muay Thai is hardly for the faint-hearted.
"To have such a sport event staged in the country should be declared illegal," Sakol Wannapong, SAT's governor, told local media recently. "It is not a sport. It is so cruel."
But Thailand's sports and tourism ministry has allowed the fight night to go ahead.
Kamol "Sukie" Sukosol Clapp, ONE Championship president Thailand, dismisses the concerns of traditionalists, saying MMA will boost Muay Thai's popularity.
A colourful scion of a wealthy Thai business dynasty, Sukie first made a name for himself in Thailand's pop music industry, where he said he faced similar opposition.
"In Thailand we had Thai country music which is huge. We did pop. But we didn't ruin country music, it went parallel. I feel it will be the same thing with MMA and Muay Thai," he told AFP.
Prawit, meanwhile, says the average Muay Thai fan is not bogged down in the dispute. They just want to see Dej win.
He said: "It's a hugely important fight. He's defending his belt in his home country and Thai people will be behind him."