King Rama IV of Siam (Thailand) (1851–68). Mongkut remained a Buddhist monk for 27 years following the usurpation of the throne by his elder brother Pra Nang (Rama III) in 1824. After ascending the throne, he made a crucial contribution to the maintenance of Siamese independence at a time when the rest of South-East Asia was falling under European influence. His enlightened policies were continued by his successor, Chulalongkorn.