The heir to the Thai throne, Crown Prince Maha Vajiralongkorn, was for years known for his colourful private life and frequent trips overseas, but as his father's health declined he adopted a more prominent public role in the politically febrile kingdom.

All eyes are now on the 64-year-old prince after the death on Thursday of his father King Bhumibol Adulyadej, who was the world's longest-reigning monarch.

He inherits one of the world's richest monarchies, protected by one of the harshest royal defamation laws on the planet.

But the twice-divorced prince will also sit as the constitutional head of a deeply polarised nation, which is trapped in a seemingly endless cycle of coups, protests and bouts of political violence.

Bhumibol was widely adored and seen by many as a semi-divine figure in a rule that arched over the lives of most Thais.

Vajiralongkorn has yet to attain such popularity and unlike his father, his ability to operate as a unifying force ostensibly above the political fray is untested.

For years the crown prince was rarely heard from in public.

But in the twilight of his father's reign -- and with Thailand ruled by the military -- he assumed many official duties.

Last year he led two highly symbolic mass cycling events, which received blanket media coverage that thrust him centre-stage as his father's health deteriorated.

Befitting his role, the prince has not publically backed any side in the bitter politics that have engulfed his country in recent years.

But some of the "Red Shirt" supporters of ousted billionaire premier Thaksin Shinawatra and his family held the crown prince's portrait aloft at their rallies before the 2014 coup.

Experts say Thailand's political turmoil is driven by concerns among competing elites over their stakes in the future of the kingdom after Bhumibol's death.

An elite aligned to the monarchy, including much of the army and judiciary, have repeatedly crushed Thai democracy movements, fuelled in recent years by a hatred of Thaksin.

They have aimed two coups at elected governments run by Thaksin and his affiliates, accusing the Shinawatra clan of vote-buying and shameless populism.

- Into the limelight -

Born on July 28, 1952, Vajiralongkorn completed his secondary education in Britain before training at Australia's Royal Military college and joining the Thai military.

He developed a passion for flying after learning the skill in the United States, piloting fighter jets in Thailand and steering planes for national carrier Thai Airways.

But little is reported about the only son of Thailand's deceased king, for fear of breaching a strict royal defamation law which heavily restricts all conversation on the monarchy.

That law carries up to 15 in years in jail on each count of defaming the king, queen, heir or regent.

Prosecutions -- and the length of jail terms -- have surged since last May's coup with some imprisoned for more than 20-years, usually for comments made online.

READ: Thai King Bhumibol, world's longest-reigning monarch, dies - palace

Experts say the heir's approach to enforcing the lese majeste legislation will illustrate much about his vision for the monarchy.

"Will the prince implement the law, will he have it in force, or will he lighten up on criticism of the monarchy?" said Paul Handley, author of the unauthorised biography 'The King Never Smiles', a book about Bhumibol banned in Thailand.

"He has the internet to go up against, he has TV, satellite TV you can't fight that. Will he try to protect himself? We don't know."

A fan of the outdoors, the crown prince led tightly choreographed mass cycling events through Bangkok in August 2015.

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In cycling lycra, helmet and sunglasses, he was followed by a who's who of Thailand's key political players including coup-making army chief turned premier Prayut Chan-O-Cha, and several other junta members.

The powerful head of the privy council, Prem Tinsulanonda, watched the start of proceedings from under an awning as crowds shouted "Long live the crown prince!"

Wives, scandals and jet planes

A second mass bike ride took place in December 2015.

But the events were tainted by a corruption scandal when a number of senior officials, including in the military and police, were charged with lese majeste for allegedly using their connections to the prince to profit from the events.

Two of those people, including a fortune teller once close to the prince, died in military custody in the days after their arrest.

That murky episode came several months after the dramatic fall from grace of Vajiralongkorn’s ex-wife, Princess Srirasmi, in another scandal that gave the Thai public a rare glimpse into palace intrigue.

At least eight of the former princess's family members were imprisoned on lese majeste charges -- including her elderly parents, her elder sister and brother-in-law, two brothers and a nephew.

They were also accused of using their ties to the monarchy for personal gain.

While she was not jailed, Srirasmi was swiftly stripped of her royal title and then divorced by the prince.

The pair had married in 2001 in a private ceremony and Srirasmi gave birth to a boy, Dipangkorn Rasmijoti, four years later.

The crown prince also has a daughter from his first marriage in 1977 to his first cousin Princess Soamsavali Kitiyakara -- a union which ended in divorce in the 1980s.

Vajiralongkorn is believed to spend significant periods of time overseas, particularly in Germany, where his personal Boeing was briefly seized in 2011 as part of a financial dispute between the Thai government and a German company.

It is on home soil where he now faces the challenge of leading a monarchy in a divided nation where most have known no other king than his father.