The Thai Dog is a very ancient breed maybe dating back 3000-4000 years ago, according to some archaeological drawings. These drawings show a dog with a sickle tail and erect ears, but no ridge.
It would seem these dogs were around well before any history was documented in Thailand. And the earliest written documentation, comes from an ancient manuscript of the period of King Songthan of Ayuttaya (1611 to 1628) who describes the Ridgeback as follows:
"The dogs are big. They are more than two sawk tall (one sawk is a traditional measurement which equals the length from an adult's elbow to his finger tips). They appear in a variety of colors. And each dog has a ridge on the back.They are fierce. They are loyal to their masters. They are able to feed themselves, digging the earth in search of small prey. They like to follow their owner, to hunt in the wood. When they catch an animal they will bring it to their master. They are loyal to the entire household. They love their companionship. They go everywhere with their masters, even as far as the big Yang tree. They are powerful and fearless.... Their ears are pointed erect and their tails stand like the swords of tribesmen... "