The succession of Thai monarchs began with Si Inthrathit at the establishment of the first Thai kingdom in 1238. With brief interruptions, 55 monarchs have ruled over four successive kingdoms, the current monarch being Vajiralongkorn (Rama X) of the Chakri dynasty.

Titles and naming conventions

In the Sukhothai Kingdom, the monarch used the title Pho Khun, and monarchs who reigned over the period of decline after Ram Khamhaeng the Great used the title Phraya. In the Ayutthaya Kingdom and afterward, thanandon, the system of Thai royal titles, determines the style of the monarch's full regnal name (which includes the title), consisting of two interconnected parts: Western nations referred to the monarch as the "King of Siam", regardless of Thai titles, since the initiation of relations in the 16th century. Mongkut (Rama IV) was the first monarch to adopt the title when the name Siam was first used in an international treaty. When the kingdom's name was changed to Thailand, the monarch's Western title changed accordingly.

Sukhothai Kingdom (1238–1438)

Tai peoples migrated into mainland Southeast Asia in the 8th–10th centuries. In the years after, Northern Thai groups established mueang that evolved into larger states, such as Ngoenyang. However, it was not until the decline of the Khmer Empire in the 13th century that a Central Thai kingdom politically and culturally related to modern Thailand was first founded.

Phra Ruang dynasty (1238–1438)

The Phra Ruang dynasty was the only royal lineage that ruled over the Sukhothai Kingdom, the first Central Thai state. Established by Si Inthrathit in 1238, who declared independence from the Khmer Empire, the dynasty laid the foundations for Thai society. Under Ram Khamhaeng the Great, the initial Thai script was invented and Therāvada Buddhism was established as the state religion. The dynasty is named after the Traiphum Phra Ruang, a Buddhist cosmology book written by Maha Thammaracha I. During his reign, the kingdom was invaded by Ayutthaya, a neighboring Thai state, becoming a tributary during the reign of Maha Thammaracha II. In the Sukhothai Kingdom, the monarch ruled from the city of Sukhothai, while the heir presumptive would occasionally be named uparaja, or viceroy, and ruled in Si Satchanalai. In 1438, Ayutthaya annexed Sukhothai at the death of Maha Thammaracha IV when Borommarachathirat II of Ayutthaya named his son Prince Ramesuan uparaja. In Ayutthaya, the tradition would evolve into the Front Palace system.

Ayutthaya Kingdom (1351–1767)

The Aytthaya Kingdom was a result of a unification between two states: the Kingdom of Suphannaphum (Suphanburi) and the Kingdom of Lavo. Though the Kingdom of Lavo was originally a Mon kingdom, the migration of the Tai peoples into the Chao Phraya basin replaced the original Mons, consequently becoming the governors of these regions. This resulted in the capital moving from Lavapura (Lopburi) and Suphannaphum (Suphanburi) to Ayodhya (Old Ayutthaya), a new capital. Later on, the Kingdom of Nakhon si Thammarat came under the influence of Ayutthaya after seceding from Sukhothai, and Sukhothai losing influence and coming under Ayutthayan influence. This conflict would last long into the history of Ayutthaya Kingdom, where families from the four major regional kingdoms vie over the throne of the kingdom. These kingdoms are: Kingdom of Nakhon Si Thammarat, Kingdom of Sukhothai, Kingdom of Lavo, and Kingdom of Suphannaphum. The Kingdom of Sukhothai was integrated into the Kingdom of Ayutthaya along with its noble famlies.

Pre-Ayutthaya era (Ayodhya period)

1st Uthong dynasty (1351–1370)

1st Suphannaphum dynasty (1370–1388)

As previously mentioned, the kingdom of Ayutthaya was the result of the unification between two federations: Lavo and Suphannaphum. The ruling dynasty of Lavo gave rise to the Uthong Dynasty, in which the Suphannaphum dynasty came from the Suphannaphum federation. This federation held significant influence within the kingdom leading them to take control of the throne in 1310.

2nd Uthong dynasty (1388–1409)

2nd Suphannaphum dynasty (1409–1569)

Sukhothai dynasty (1569–1629)

Prasat Thong dynasty (1629–1688)

Ban Phlu Luang dynasty (1688–1767)

Thonburi Kingdom (1767–1782)

Thonburi dynasty (1767–1782)

Rattanakosin Kingdom (1782–present)

Chakri dynasty (1782–present)

Timeline of monarchs

Family tree of the Thai monarchs

Used regnal names