In a country that has grown ­accustomed to political chaos – it has seen some 20 coup attempts including 12 successful ones in the last century – the reverence for Bhumibol flowed from his ability to ostensibly stay above the fray and exert moral authority to restore calm each time the waters became choppy.

For outside observers, the open and almost fawning adulation for the king across political and socio-economic divides might give the ­impression that ­absolute royal rule did not give way to a constitutional monarchy in 1932.

The image of the bespectacled, rarely smiling king is omnipresent in Thailand, seen everywhere from currency notes to vast billboards on buildings and lamp posts.

Critical observers of the monarchy say the veneration of ­Bhumibol is engineered to ­advance the political interests of opportunistic courtiers, and enforced by the hugely controversial royal defamation law that makes criticism of the monarch punishable by up to 15 years in jail.

Patrick Jory, an Australia-based historian who focuses on the Thai monarchy, said the king’s death “is an end of an era for Thailand, but also the start of a new one”. “A state-imposed personality cult since the cold war has transformed the king into a symbol of the Thai nation and, for many Thais, a future Buddha,” said Jory, a lecturer at the University of Queensland.

Bhumibol in 2005 hinted at his own position on criticism of the monarchy.

“When you say the king can do no wrong, it is wrong,” he said in a speech on the occasion of his 78th birthday.

“I want them to criticise because, whatever I do, I want to know whether people agree or disagree,” he said in the presence of dignitaries.

“If you say the king cannot be criticised, it means the king is not human.”

Facing strident criticism was the least of worries for a young Bhumibol, whose rise to the throne at age 19 was under tragic circumstances rather than pre­ordained destiny.

Bhumibol was born on ­December 5, 1927 in suburban Boston, making him the only known monarch born in the United States.

His father was Prince Mahidol, the 69th son of the Siamese king Chulalongkorn – immortalised in the Western world by the film The King and I.

His mother, Sangwan, was a commoner from a poor family who was part Chinese.

The family had gone to the US in the mid 1920s, when Mahidol studied for an advanced medical degree at Harvard University.

The sitting king in Bangkok at that time, Prajadhipok, abdicated in 1935 in favour of Ananda, Bhumibol’s 10-year-old elder brother, after he became disillusioned with the constitutional monarchic system imposed.

Bhumibol’s world would abruptly change nine years later with the throne thrust upon him after Ananda was found shot dead in his palace bedroom. The ­circumstances of Ananda’s death remain unresolved.

Mahidol died young, and the children moved with their mother to Lausanne, Switzerland, where they picked up French, German and Latin.

Bhumibol, who enrolled at the Lausanne University in a science course, decided to change his ­major when his brother died and the role of sovereign was handed to him.

When he returned to university in 1946, he enrolled in a customised course covering political science, government and law.

Bhumibol ­returned to Thailand in 1950. He quickly gained favour with the people for his work to provide basic health care and education for the rural poor.

He held four patents, including one awarded in 2003 for his development of an artificial rain-making technique.

Observers credit the king with providing vital stability in the country in the 1960s and 1970s as communist regimes overran neighbouring countries.

Bhumibol’s ascendancy also saw the rapid rise of the financial clout of the monarchy. The Thai palace, through its stewardship of the Crown Property Bureau, is seen as one of the world’s wealthiest monarchies.

A 2015 study showed it holds upwards of US$44 billion in ­assets, including stakes in Siam Commercial Bank and Siam ­Cement as well as large tracts of prime land in Bangkok.

For international observers, Bhumibol’s most prominent act as king came in 1992, when he ­intervened following a political standoff over an attempt by a ­former junta leader, Suchinda Kraprayoon, to become premier.

Dozens of protesters were shot dead in protests against Suchinda in the bloodiest bout of political violence in decades.

Television images showed Bhumibol seated in a gilt-trimmed chair chastising Suchinda and the protest leader, Chamlong Srimuang, who were on their knees in front of him.

The king’s waning health over the past decade has coincided with increased political turmoil.

In 2006, a year after Bhumibol’s speech about the lese-majeste law, the military staged its first coup in 15 years against the government of the populist telecom billionaire turned prime minister, Thaksin Shinawatra.

That spurned sustained protests between Thaksin’s followers, rural dwellers in the country’s north and northeast, and the royalist elites in Bangkok. Thaksin’s sister, Yingluck Shinawatra, came to power in elections in 2011, but the military again intervened in 2014 to depose her.

The junta, in power today under the stewardship of former general Prayuth Chan-ocha has promised elections next year. A military-scripted constitution was approved by voters in an ­August referendum.

There is a widespread consensus among political observers that Bhumibol’s named successor, the 64-year-old Crown Prince Vajiralongkorn, will be enthroned.

Palace watchers have brushed off previous talk that he was not favoured by the ruling elite.

“Instability, rather than a given figure who occupies the position of king, is the threat that the Bangkok elite fear,” said Tyrell Haberkorn, a Thai politics expert at the Australian National University.