Borommatrailokkanat (Thai: บรมไตรโลกนาถ,[1][2][3][4] pronounced [bɔ̄ː.rōm.mā.trāj.lôːk.kā.nâːt], Sanskrit: Brahmatrailokanātha) or Trailok (1431–1488) was the king of the Ayutthaya Kingdom from 1448 to 1488.

He was the first Thai king to possess a "noble" or white elephant, which, according to Buddhist belief, was a "glorious and happy sign".

[5] His reign was also known for massive reforms of Thai bureaucracy and a successful campaign against the Lan Na Kingdom to the north.

Some authors claim that his mother was a princess of the Sukhothai Kingdom, daughter of Sai Lue Thai.

According to historian Michael Vickery, however, this is not verifiable in historic sources and may be due to a misreading or misinterpretation of a chronicle.

He also stopped the tradition of appointing royal princes to govern cities, as they had always clashed with each other in times of succession.

Originally they were meant to serve as simultaneous military and civil Greater Officers of State for the north and south, respectively.

[11] Borommatrailokkanat adopted the position of Uparaja, translated as "Deputy-King", "viceroy" or "underking", usually held by the king's senior son, or full brother, or the sons of their queens, in an attempt to regularize the succession to the throne — a particularly difficult feat for a polygamous dynasty.

He appointed his eldest son Uparaja of Ayutthaya while he lived in Phitsanulok for twenty-five years, keeping Chiang Mai under control.

In 1456, Yutthitthira sought Tilokkarat’s support and led the Lan Na armies to capture Sukhothai and proceeded further towards Ayutthaya.

In 1485, Borommatrailokkanat appointed his son Prince Chaiyachettha (later Ramathibodi II) as the Uparaja and King of Sukhothai.