king of Siam (1824–51) who made Siam's first tentative accommodations with the West, and under whom the country's boundaries reached their maximum extent.

Rama III was the eldest son of King Rama II by a royal concubine, and in his youth he was given responsibility for overseeing foreign trade and relations. On his father's death in 1824, Rama III was much older and more experienced than his younger brother Mongkut (q.v.; who because he was born of a queen had a stronger claim on the throne), and the accession council chose him to succeed to the throne. His earlier experience enabled him to withstand British demands presented by the Burney mission (1826) and conclude a treaty that established regular trade with the West but yielded none of Siam's independence.

In the 1830s and '40s Rama III was preoccupied mainly with Laos and Cambodia and intervened in the latter to forestall colonization by the Vietnamese. Recognizing the strong claims of Mongkut to the throne, Rama III refrained from naming an heir apparent, and Mongkut succeeded him in 1851, as the kingdom headed for a new confrontation with the West.