The world's longest-serving royal sovereign until his death last year at the age of 88, Bhumibol rebuilt a near-extinct monarchy into one of the wealthiest and most powerful on the planet -- and one whose roots go deep into modern-day Thailand.
Uncertainly looms about how his heir, King Maha Vajiralongkorn will lead the monarchy.
"How the new king intends to reign is what Thai people are observing because it will have much to say about how their political life will be," Thitinan Pongsudhirak, politics professor at Chulalongkorn University, told AFP.
Thailand's absolute monarchy was abolished in 1932, but under the official title of King Rama IX, Bhumibol exercised a powerful moral authority and also a political one as his reign matured -- albeit often away from the public eye.
Crowned in 1950, many analysts attribute his longevity during an era strewn with political violence to deep ties with a military that relied on his official endorsement of their repeated coups.
The army's latest power grab was in May 2014, when it toppled the elected government of Yingluck Shinawatra.
That coup came just eight years after her billionaire brother Thaksin was overthrown as premier in 2006.
Right up until his death, Bhumibol was seen as a unifying figure in the deeply divided country.
"Because of King Bhumibol's immense moral authority, the Thai people will want King Vajiralongkorn to succeed," Thitinan said.
An untested ruler, King Maha Vajiralongkorn, or Rama X, has spent much of his adult life in Germany and has not attained the widespread popularity of his father.
Image crafting
Helped by well-publicised rural development projects, the soft-spoken, bespectacled King Bhumibol enjoyed an image of a benevolent moral force.
That reputation was carefully embossed by ritual, a well-oiled propaganda machine and a tough royal defamation law.
In 2011, Forbes Magazine rated Bhumibol as the world's richest monarch.
But despite his wealth, the keen saxophonist, photographer and sailor was seen as in touch with ordinary Thais.
The reverence resonates deep into public and private life.
Young people are taught about Bhumibol's good works at school, cinema-goers have to stand for the royal anthem at the start of films, while people prostrated themselves, or crawled, in his presence.
Giant portraits of the king -- and queen -- pepper towns and cities across the country, while photos of the monarch adorn many Thai households.
Nearly 12 million mourners visited the royal reception hall where his body lay in state.
Sailing and Saxophone
Born on December 5, 1927 in the United States, Bhumibol came to the throne aged 18 in 1946 when his brother was shot dead in mysterious circumstances at the Royal Palace in Bangkok.
He was crowned four years later after finishing his studies in Switzerland.
The same year, he married Queen Sirikit and they had four children -- three girls and a boy.
A man of widely publicised interests, Bhumibol won a gold medal for sailing at the Asian Games in 1967 and was behind some 3,000 rural development projects.
But the hurly-burly of Thai politics dominated his long reign.
In the 1970s the king intervened during several political crises.
His most spectacular arbitration came in 1992 when he waded in between the military and pro-democracy protesters the leaders of the two camps bowed down before him and made peace, in a televised act of deference.
The emergence of Thaksin Shinawatra, who was voted in as premier in 2001, shaped the twilight of his reign.
Bhumibol remained largely silent during a military crackdown on pro-Thaksin "Red Shirt" protests in 2010 that left about 90 people dead and hundreds wounded in the capital, despite calls from some opposition figures for his intervention.
With avenues for criticism growing, particularly on social media, authorities strictly enforced Thailand's harsh lese majeste laws, which carry a jail term of up to 15 years on each count for defaming the royals.
Dozens of cases have been driven through the courts since the 2014 military coup.
The ruling junta says it is duty-bound to protect the reputation of the monarchy.
But critics say the law has been used as a tool to crush dissent and straitjackets all public discussion on the monarchy.
"Unlike other modern monarchies, it is impossible to tell exactly how popular the Thai monarchy is," said analyst and historian David Streckfuss, author of a book on Thailand's lese majeste laws.
