He was born in Ayutthaya on March 20 1737 as son of Phra Aksorn Sundara Smiantra, a noble man in the Ayutthaya kingdom. His birth name was Thong Duang. After getting education in a Buddhist temple, his father sent him to serve as a page for the later king Utumporn. There he met his friend Sin, the later king Taksin. After the fall of Ayutthaya he joined Taksin's army, and was known as Chao Phraya Chakri. The name Buddha Yodfa Chulaloke was given posthumously by king Nangklao (Rama III).
While Taksin's general, he conquered Vientiane in 1778/79, putting the country under vassalage, and removing its Emerald Buddha to Thonburi. In 1782, when Taksin was declared mad after a coup d'etat and was later executed, he assumed power, establishing the Chakri dynasty. He was crowned on April 6; the date is now a public holiday in Thailand.
King Rama I continued Taksin's task of saving the newly reunited country from attack by Burma, but he also reestablished the traditions of the country by salvaging Buddhist texts lost in the chaos after the sacking of Ayutthaya. He also built the new capital Bangkok and in his palace the Wat Phra Kaew to house the Emerald Buddha, and created a new code of laws, the Book of three seals. As literature was his passion he also wrote a Thai version of the Ramayana epos called Ramakian.