They formed part of a hierarchical social system which developed from the time of the Ayutthaya Kingdom (14th century – 1767), through the Thonburi (1767–1782) and early Rattanakosin (1782 onwards) periods.
While the use of noble rank and title words are found in the documents of many early Tai city states including Sukhothai, the earliest extensive descriptions are from the administrative reforms introduced in 1448 by King Borommatrailokanat of Ayutthaya, which by then had become the dominant polity in the region.
The reforms established official titles for high-ranking ministers of the chatusadom system, and the rank of phra was added to the previously used khun and nai, in order to accommodate the expanding machinery of government.
Unlike in European aristocracies, Thai noble titles were not inherited, but individually granted by the king or his ministers based on personal merit.
This practice became especially influential from the 17th century, when war subsided and commerce flourished, leading personal patronage to displace martial ability as the determining factor for promotions.
His successor Vajiravudh (Rama VI, r. 1910–1925) introduced a military-style promotion-based rank system, superseding the traditional titles, though they could still be granted at the king's discretion.
[2][3] Following the abolition of absolute monarchy in 1932, royal decrees issued during the government of Plaek Phibunsongkhram in 1942 abolished the use of noble titles and the rank system.
Historical references to holders of shared titles conventionally include the person's birth name in parentheses, e.g. Chao Phraya Chakri (Mut), who was chief minister under King Taksin.