was the fifth monarch of Siam under the House of Chakri. He was known to the Siamese of his time as Phra Phuttha Chao Luang (พระพุทธเจ้าหลวง – The Royal Buddha). He is considered one of the greatest kings of Siam. His reign was characterized by the modernization of Siam, immense government and social reforms, and territorial cessions to the British Empire and French Indochina.