The 92-year-old from the southern Mekong Delta region is the proud owner of 5m long dreadlocks, owing to his belief in a faith that prescribes leaving untouched what a person is born with.
"I believe if I cut my hair I will die. I dare not to change anything, not even combing it," Chien told Reuters in his village about 80km west of Ho Chi Minh City.
"I only nurture it, cover it in a scarf to keep it dry and clean and looking nice."
Chien, who worships nine powers and seven gods, believes it was his calling to grow his hair, which he bundles up under an orange turban.
He was required to trim it when at school, but left after third grade and decided never to cut, comb or wash it again.
"I remembered my hair was black, thick and strong. I combed it, untangled it to make it smooth. But when I heard the calling from the divine power, I knew immediately that I was chosen," he said.
"I touched my hair and overnight it has became really hard. It has attached to my head and became a thing of its own."
Chien follows a near-obsolete faith known as "Dua", the coconut religion, named after its founder who claimed he survived only on coconuts to retain his vitality. Dua is banned in Vietnam and categorised as a false belief.
Chien's fifth son, Luom, helps him to manage his giant locks.
He too believes in the connection between hair and mortality, having seen a man pass away after trying to re-attach his hair with string.
"These things look simple but they are sacred," said 62-year-old Luom.