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Borommaracha I (Thai: สมเด็จพระบรมราชาธิราชที่ 1, RTGS: Boromma Rachathirat I) or Khun Luang Pa Ngua (Thai: ขุนหลวงพะงั่ว) (1370–1388) was the third king of Ayutthaya Kingdom. His name Khun Luang Pa Ngua literary means the fifth prince.
As the lord of Suphanburi, a powerful rival of Ayutthaya, he forced King Ramesuan from power and took the throne of Ayutthaya. Known as a great warrior, his reign marked the expansion of Ayutthaya to the north. He suppressed a rebellion in Sukhotai (1371-78) and subjugated major northern powers such as Phitsanuloke. Invading Chiengmai, his forces were defeated and repulsed at the Battle of Sen Sanuk, near Chiengmai.
After his death in 1388, his son, Thonglun reigned for only a week. Ramesuan, who had previously retreated to Lopburi, returned and toppled him. Ramesuan eventually assumed the throne, as the king for the second time.
- p. 431, 'The Collins Encyclopedia of Military History' (4th edition), Dupuy & Dupuy, 1993.