Rama Khamhaeng (ca. 1239-ca. 1299) was king of Sukhothai in Thailand and the founder of Thai political power in central Indochina. He remains the Thai model of the patriarchal ruler.

Rama Khamhaeng was the third son of King Sri Indraditya, who had seized power in Sukhothai from the Cambodian empire of Angkor between 1219 and 1245. When Rama's brother, King Ban Müang, died, he inherited a small kingdom in the foothills of north-central Siam. By a combination of shrewd alliances, careful diplomacy which ensured the neutrality of rivals, and forceful military campaigns, especially in the 1290s, he extended his kingdom to Luangprabang and the Vientiane region in Laos to the north, westward to the Indian Ocean coast of Burma, and south to Nakhon Si Thammarat on the Malay Peninsula.

Apart from colorful but unreliable myth, almost all that is known of Rama Khamhaeng comes from his great inscription of 1292, the oldest known inscription in the Thai language and script. That lengthy document portrays the King as a father to his subjects, available day and night to petitioners for justice, liberal in his gifts and in his treatment of his vassals, merciful in warfare, and pious in his devotion to Buddhism. His state is depicted as happy and prosperous: "This state of Sukhothai is good. In the waters there are fish; in the fields there is rice." Implicit in this account are policies strongly in contrast to the bureaucratic complexity, impersonality, and economic rigidity of Angkor. Sukhothai under Rama Khamhaeng was a simple state with no pretensions, where justice was to be had, trade could flourish, and peace would reign. These policies, and the strong leadership of the King, were responsible for the kingdom's phenomenal success in detaching so much territory from mighty Angkor. Still experimenting with political institutions, however, Rama Khamhaeng's son and successor, Lö Thai (reigned ca. 1299-1346), was unable to hold the state together in the face of challenges from other Thai princes to the south, and the kingdom of Ayudhya (1350-1767) ultimately reduced Sukhothai to a province (1438).

The 1292 inscription, lost for many centuries, was rediscovered by King Mongkut, then a Buddhist monk, in 1834, and the image of Rama Khamhaeng, resurrected, became a powerful ideal for subsequent rulers.