King Rama I was formerly known as Thong Duang. Following the fall of Ayutthaya in 1767, he entered the service of Phya Tak Sin and fought by his side in almost every campaign until the latter became King Tak Sin. After King Tak Sin was deposed in 1782, Thong Duang was chosen as King, becoming the founder and first ruler of the Chakri Dynasty. In the year of his accession, he moved the capital of Thailand from Thonburi to the city of Bangkok, the opposite side of the Chao Phraya River. During his reign, the Grand Palace was constructed and the Emerald Buddha was installed in the Royal Chapel. Many historians have stated that the modern Siam dates from his reign. 

Although the absolute monarchy was still the form of government, King Rama I's rule was endowed with the Ten Kingly Virtues. He devoted himself to a thorough reorganization of the administration that had fallen into a chaotic condition since the destruction of Ayutthaya. However, the government of King Rama I was still highly centralized with officials whom he could trust to the fullest measure in charge of the various offices. It was suitable for the country and the people of that period since education was practically non-existent for the common people. He then undertook a reform of the Buddhist Church. The monks' discipline was tightened in order to maintain a respectable standard of behavior. The Buddhist Scripture, or the Tripitaka, was assiduously revised at royal expense. This was a necessity since most of the authoritative books on the subject had been scattered or lost in the conflagration of Ayutthaya. The King built and restored twelve monasteries, in addition to a monastery called Wat Prajetubon or Wat Po at the rear of the Royal Palace.

King Rama I set up a commission of legal experts to revise the country's laws in 1805. The result of its work was the Laws of Three Seals or the Law Code of 1805-1808.

The reign of King Rama I fostered a literature renaissance after the ransacking of Ayutthaya. In spite of such pressing matters as the war with Burma, he found time to uplift the dignity of Thai literature. Not only did he encourage the writing of prose and poetry, but he also himself composed poems so well that he is now accepted as a legitimate poet in the history of Thai literature. He took upon himself the task of rewriting and revising the Ramakien and the Inao. The Ramakien is the Thai version of the Ramayana that is a great epic of Hindu inspiration. It is ranked as a literary work of enormous popularity, and is the only one used in the classical masked play called "Khon".