Nangklao () or Rama III (31 March 1788 – 2 April 1851) was the third monarch of Siam under the House of Chakri, ruling from 21 July 1824 to 2 April 1851. He succeeded his father, Rama II, as the King of Siam. His succession was unusual according to the traditions because Nangklao was a son of a concubine rather than that of a queen. His accession was perceived by foreign observers as having usurped the prior claim of Prince Mongkut, who was a legitimate son of Rama II born to a queen, Srisuriyendra. Under the old concept of Thai monarchy, however, a proper king must emulate Maha Sammata in that he must be "elected by the people." Ironically, Prince Mongkut may have later contributed to this misconception, when he feared that his own accession might be perceived by foreign observers as a usurpation.