U-thong was the first king of the kingdom Ayutthaya (now part of Thailand), reigning from 1351 to 1369. He was known as Prince U Thong (meaning "source of gold") before he ascended to the throne on March 4, 1351 to become King Ramathibodi I whose position was likely secured by political marriage and family ties.
A Renowned Legend stated that U-thong was an ethnic Chinese who was so successful in trade that he became influential enough to rule the city of Phetchaburi, a coastal town of the Gulf of Thailand, before sailing up to Ayutthaya.
He was married to a daughter of the ruling family of the Suphanburi Kingdom, and may have also married into an alliance with the rulers of Lavo Kingdom (also known as Lopburi). His son also became the ruler of Ayutthaya, King Ramesuan, though later abdicated by King Ramesuan.