Rajadhirat was a Mon king known for his military prowess.

Rajadhirat succeeded his father Binnya U as ruler of Pegu after a succession struggle in 1383. He unified Lower Burma during the 1380s. From 1385 to his death around 1421, Rajadhirat's kingdom of Pegu and the kingdom of Ava in Upper Burma most notably during the reign of King Minhkaung were engaged in a continual state of warfare known as the Forty Year Mon-Burmese War described in the chronicle Yazadiyit Ayeidawbon in Burmese. The use of scorched earth tactics by both sides was a prominent feature of this warfare.

Rajadhirat's daughter became the Mon Queen Baña Thau (Burmese: Shin Saw Bu) several years later and reigned in relative peace starting a revival in Theravada Buddhism.

The story of Rajadhirat's reign is recorded in a classic epic that exists in both Mon language and Burmese language forms. During the reign of the Thai king Buddha Yodfa Chulaloke (1782-1809), this epic was translated into the Thai language by court minister and author Phra Khlang and is well-known in Thailand even today.