The snakes are called “Phaya Nak” in Thai (usually translated as Nagas in English) and they are a powerful, semi-divine, supernatural race in Hindu and Buddhist mythology. Depictions can have single or multi heads, although the multi headed Nagas are usually used to represent a Naga King.

In Thailand Phaya Nak are associated with rivers, caves, rainfall, wealth, and protection. The Mekong River is said to have been created by the slithering of a Naga and an oracle is asked of the Nagas every year at the Thai Royal Ploughing Ceremony to see what the rainfall will be like in the upcoming year.

There are also caves in Thailand that are sacred to the Nagas and people will make pilgrimages to them to make offerings and ask for boons.

Nagas are also known as protectors in the Thai Buddhist tradition. The Vinaya Sutra states that shortly after his enlightenment, the Buddha was meditating under a fierce storm that threatened to wash him away. Out of the earth came the multi headed Naga King and sheltered the Buddha from the storm, thus preserving his life and the Dharma. It is not uncommon to see statues of the Buddha meditating under this multi headed Naga.

Other common depictions of the Phaya Nak in Thailand include Naga heads at the end of temple roofs, the railings of stairways leading into temples, and on the Thai royal barges.

Also, although this post in mainly focused on Thailand, the Nagas are not limited to Thailand and have a presence in most south and southeast asian folklore.