Sudhammaraja

Sudhammarāja (Thai: สุธรรมราชา), a monarch of the 10th century, is recorded in the Ayutthaya Testimonies as the ruler of Phitsanulok and Phra Nakhon Sawan Buri (พระนครสวรรค์บุรี; identified as modern Sankhaburi in the Phraek Si Racha historical region). He is described as having ascended the throne at the age of 15, succeeding his father, Sai Nam Peung, and ruling the polity for a period of 35 years. Based on retrospective chronology, his reign is estimated to have extended from 922 to 957 CE, suggesting his birth year was approximately 907 CE. Sudhammarāja entered into matrimony with Śrīprajārājadevī (ศิริประชาราชเทวี); however, no extant record provides information concerning their progeny.

The reign of Sudhammarāja is notably associated with the establishment of Phitsanulok, to which he subsequently transferred his seat of power. Although the Ayutthaya Testimonies does not explicitly specify the precise date of Phitsanulok's foundation, it refers to another monarch of Phra Nakhon Sawan Buri named Sindhob Amarin, who is likewise recorded in the Northern Chronicle. According to the Northern Chronicle, Sindhob Amarin reigned for 59 years before he died in 996 CE, indicating that his accession likely occurred around 937 CE, assuming the year of Sudhammaraja's departure to found Phitsanulok. This chronology places Sindhob Amarin's reign after that of Sudhammarāja; however, the compiler of the Ayutthaya Testimonies identified Sindhob Amarin with Bharattakabba, who is recorded to have ruled before Sudhammarāja's father, Sai Nam Peung.

The relocation of Sudhammarāja occurred subsequent to the conquest of Lavapura of Lavo by King Sujita of Tambralinga in 927. Following this event, several polities situated within the regional river valleys—most notably Suphannaphum—are recorded as having confronted military campaigns undertaken by Tambralinga, led by Sujita's son, Kampoch. Sudhammarāja's reign at Phitsanulok was succeeded by Visnuraja, a monarch descended from King Padumasūriyavaṃśa. The lineage of Visnuraja subsequently extended to the Phra Ruang dynasty of the Sukhothai Kingdom and the Lavo dynasty of the Ayutthaya Kingdom.