The first written mention of the Gunman Thong is in Sunthorn Phu's "The Story of Khun Phaen and Khun Chang". The story is set in Ayutthaya about 500 years ago and was well known as an oral legend before being written down in the 19th century.

Khun Phaen was a warrior hero who required a powerful spirit to protect him in battle.
His Mia Noi, Bua Klee, died while still pregnant.
Normally at that time people were cremated shortly after death, but women who died in childbirth were buried with special ceremonies in order to stop their ghosts wandering.
The ghost of a woman who died in childbirth, Phee Tai Tong Klom, is especially ferocious and greatly feared.

K. Phaen dug up the corpse of Bua Klee and extracted the foetus and took it directly to the Bot of a nearby temple to prepare it for the ritual which would capture it's spirit and make it serve him.

The body of the foetus must be baked dry before the spirit will re-enter it.
K. Paen prepared the ritual, it is still performed in almost exactly the same way today.
He took consecrated wood to make a bed for the corpse, lit three candles, and laid the corpse on the bed.
He placed yantras on the body, a Vishnu Yan on its head, another on its belly, a royal yan under the corpse, and a Dharani yan on the ground.
He took sai sin, sacred white thread, and wrapped it around the bed and the corpse tio keep malign influences away.
The ghost of the mother was prevented from entering the temple as the strongest ghosts are forbidden from entering sacred places.
He set posts at each corner of the bed and placed scared flags on each post. Taking consecrated wood he lit a fire and carefully moved the foetus so that it would bake slowly and dry in the heat of the fire.

To bring the spirit back to the body he recited mantras throughout the night, just as dawn broke the foetus, now dried to a golden brown colour rose from the bed and spoke to Khun Phaen.
He declared himself willing to obey any command K. Phaen gave him. Khun Phaen named him Guman Thong, the Golden Boy.

Today few Guman Thong are made from real foetuses although some monks/magicians will still do so for a hefty fee.

Luang Por Tim of Wat Lahanrai made Guman Thong from human ashes until quite recently but was made to stop as it was seen as immoral.
There was a recent newspaper article about a Cambodian man who killed a pregnant woman to get a foetus for this purpose and a well known Thai black magic practioner, filmed himself making a Guman Thong from a fetus, after this practitioners arrest for fraud the film he made was shown on Thai TV last year.

Most are now made from wood or metal and have the appearance of a topknot-wearing little bit dressed in traditional Thai style.

The spirit inside must still be the spirit of a little boy and normally the maker of the Guman Thong will petition Phya Mutjarai, the King of Death for a soul to occupy the Golden Boy.
The soul of the child must be well fed and cared for and the owner must perform several daily rituals and chants to ensure that the spirit does not turn against him. As the spirit is the spirit of a human child it is subject to the laws of Karma and rebirth.
At some time the child will be reborn and the spirit will need to be set free.
It's an act of great merit to release the spirit of the Golden Boy at the right time and there are a series of rituals for doing this.
Keeping the spirit imprisoned is a heinous act but many people still do it.

Only a few monks know the mantras required to imprison the spirit in a Guman Thong although there are many fakes.
A genuine Guman Thong maker can show the lineage of teacher who taught him. The most respected Kuman Thong makers of recent times are LP Hon of Wat petchaburi, LP Boon of Wat Klan Bangkaew, A. Yaem and LP Tae Kongtong of Wat Samnam, A. sakorn and LP Tim of Wat Lahanrai, and LP Poon of Wat Pailom.