A common mistake made by visitors to Thailand is to assume that Brahma shrines are a “four faced Buddha”. This is probably a natural assumption made on the grounds that Thailand is a Buddhist country, indeed, Thailand has the highest percentage per population of Buddhists in the world, so it’s a mistake which can easily be forgiven.
Brahma shrines are very common throughout Thailand, the most famous one is the Erawan Shrine in Bangkok, but you see them commonly outside hotels, government buildings, banks, large restaurants, and villages. Although Brahma is a Hindu Deity, Thais don’t worship him as Hindus, like so many other popular Hindu deities in Thailand, including Ganesh and Shiva, Brahma is a legacy both of Cambodia’s rule over Thailand many hundreds of years, ago and Indian influence, the most obvious evidence of this Hindu Legacy is in the form of Spirit Houses. The taller of the 2 spirit houses seen outside most Thai households is a called a San Phra Phoom, there are various spellings of this, you will often here it called “San Phra Phum”, inside the San Phra Phoom there is usually a Hindu Deity, he is the protector of the land.
Brahma shrines are known as San Phra Phrum or San Phra Brahm, the role of the Brahma Shrine is much the same as a spirit house, to protect and to bring good luck, you might say the the San Phra Phrum is the ultimate spirit house.
Hinduism and Hindu Deities are quite a complex subject, Brahma is seen as the creator of the world, each of his four faces, his arms and various attributes have a symbolic representation. Religion and spirituality in Thailand are also very complex, Buddhism and Hinduism are very closely related and at times intertwined, when you add Animism (spirit worship) and superstition to the mix you end up with a rather unique mixture, a sort of “spiritual fusion“.