Phrabat Somdet Phra Poramen Maha Mongkut, Phra Chom Klao Chaoyouhua, or Rama IV (October 18, 1804 - October 1, 1868) was the fourth king of Siam (1851 - 1868) of the Chakri dynasty and one of the most revered monarchs of Siam.
Thais usually call him "King Chomklao". When they mention "King Mongkut", they are talking about Wachirawudh.
Outside of Thailand he is best-known as the King in the play and film "The King and I", based on "Anna and the King of Siam" - in turn based on the writing of Anna Leonowens about her six years at his court.
In his reign, the pressure of Western expansionism was felt for the first time in Siam. Mongkut embraced Western innovations and initiated the modernization of Siam, both in technology and culture—earning him the epithet "The Father of Science and Technology" in Siam.
Mongkut was also known for his appointment of his brother, Prince Chutamani, as the second king. Prince Chutamani was crowned in 1851 as King Pinklao; and so at this time Siam had two monarchs simultaneously. Mongkut himself assured that Pinklao should be respected with equal honor to himself. Mongkut's reign was also the time when the power of the House of Bunnak reached the zenith and became the most powerful noble family of Siam.
The King and Buddhism
In 1824, at age 20, Mongkut became a Buddhist monk, according to Siamese tradition (that men aged 20 should become a monk), with ordination name Vajirañāṇo. However, the same year, his father Buddha Loetla Nabhalai died. According to succession traditions, Mongkut was to be crowned the next king. However, the nobility instead put the influential Prince Jessadabodindra, his half-brother, on the throne. Perceiving that the throne was irredeemable, Mongkut chose to stay in his ecclesiastic status to avoid political intrigues.
Mongkut became one of the members of royal family who devoted his life to the religion. He travelled all around the country as a monk and saw the relaxation of the rules of Pali Canon among the Siamese monks he met - which he considered inappropriate. In 1829, at Petchaburi, he met a monk named Buddhawangso who strictly followed the canon. Vajirayan admired Buddhawangso for his obedience to the canon and inspired his religious reforms.
The monk Vajirayan then established the Thammayut Nikaya or Thammayut sect in 1833. The new sect reinforced the canon law. The Thammayut sect gained royal recognition in 1902 by Mongkut's son Chulalongkorn (through Ecclesiastical Polity Act) and became one of the two major Buddhist denominations in modern Thailand. (see Buddhism in Thailand) In 1836, he became the first abbot of Wat Bowonniwet, which is sponsored by the royal family to this day. During his time as a monk, Bhikkhu Vajirañāṇo discovered Western knowledge, studying Latin, English, and astronomy with missionaries and sailors. King Mongkut would later be noted for his excellent command of English, although it is said that his younger brother, Vice-King Pinklao, could speak it even better.
As a monk and Buddhist scholar, King Mongkut worked to establish the Thammayut Nikaya, an order of Buddhist monks that he believed would conform more closely to the orthodoxy of the Theravada school. It was said that the newly-established order was tacitly supported by King Nangklao, despite oppositions to it by conservative congregations, including some princes and noblemen. Later, when King Mongkut himself became King, he would strongly support his sect. Reportedly, King Mongkut once remarked to a Christian missionary friend: "What you teach us to do is admirable, but what you teach us to believe is foolish."