Chulalongkorn was born September 20, 1853 in Bangkok as the oldest son of King Mongkut (Rama IV) and Queen Debsirinda. His father made sure his son got very good education, including European tutors like Anna Leonowens. At age 15 he joined a Buddhist monastery.
His father died when Chulalongkorn was seventeen, and on October 1, 1868, he succeeded him, however as he was still too young to rule, the chief minister Chao Praya Srisuriyawongse served as regent for four years. During this time Chulalongkorn did travel to other countries like Singapore, Java and India, to study western lifestyle and colonialism, which made him the first thai king to leave the country. Later during his reign he also visited Europe twice in 1897 and 1907.
On November 16, 1873, he was crowned for the second time. During his travels he had learned about many reforms needed to modernize his country. He managed to keep his country independent even though both France and Great Britain were colonizing most of Southeast Asia. However he had to cede some territory to these two powers, for example Laos or northern parts of Malaysia belonged to Thailand before.
King Chulalongkorn modernized the government by introducing a cabinet system, and the semi-feudal provincial administration was changed into a modern administration with provinces (changwat) and districts (amphoe) it still has today. He also abolished slavery. The first railroad of Thailand was opened in his reign in 1896 from Bangkok to Ayutthaya. He also adopted the western calendar by abolishing the tradition lunar calendar. The modern coin and banknote system was also introduced by him.
The Chulalongkorn University, founded in 1917 as the first university of Thailand, was named in his honor.