Phra Bat Somdet Phra Poraminthra Maha Chulalongkorn Phra Chunla Chom Klao Chao Yu Hua, or Rama V, 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. His reign was characterized by the modernization of Siam, governmental and social reforms, and territorial concessions to the British and French. As Siam was threatened by Western expansionism, Chulalongkorn, through his policies and acts, managed to save Siam from colonisation. All his reforms were dedicated to ensuring Siam's survival in the face of Western colonialism, so that Chulalongkorn earned the epithet Phra Piya Maharat.

https://en.wikipedia.org/wiki/Chulalongkorn