Sultan Hassanal Bolkiah lives in a 1,788-room palace and has a garrison of British troops on his payroll to help secure his oil-rich nation.
In 1996, late pop idol Michael Jackson was paid a reported US$17 million to give a concert to mark the sultan's 50th birthday.
His brother, Prince Jefri Bolkiah, has been embroiled in scandals that revealed a jet-set lifestyle, including allegations of a high-priced harem of Western paramours and a luxury yacht called "Tits".
This royal reputation for excess and extravagance stands in stark contrast to the religious turn that the country took last Wednesday, when the sultan introduced hudud - an Islamic penal code that calls for death by stoning for crimes such as adultery.
But according to people with inside knowledge of the royal family, Brunei's journey to hudud law, which harks back to the time of the Caliphate, has been a long time in the making.
The Sultan's spiritual influence lies some 1,400 kilometres away to the west, in Malaysia's state of Kelantan, where a Muslim cleric by the name of Nik Abdul Aziz Nik Mat resides.
"Nik Aziz is like the Pope to the Sultan of Brunei," said a Malaysian businessman with links to the inner circle of the Brunei royal family.
A Muslim intellectual with ties to Brunei echoed his words. "It is true, the Sultan has long looked up to Nik Aziz.
"This [hudud] is not a sudden thing. It is a long process, it has been a long journey," said the intellectual.
Nik Aziz is a key figure in Malaysia's leading Islamist opposition, Parti Islam se-Malaysia (PAS), which has ruled the state of Kelantan since 1990. He is deeply revered by his followers.
Known for his fatherly ways and clean image, Nik Aziz led Kelantan as its chief minister from 1990 until last year, when he stepped down, but he remains the spiritual leader of PAS.
It has long been a PAS dream to establish hudud in the state of Kelantan, and Nik Aziz has been the driving force behind this push.
PAS is now looking for parliamentary approval to implement hudud. It plans to put forward two private members' bills in parliament in June.
The state's goal was given fresh impetus by the developments in Brunei, where residents now face conviction by Islamic courts and fines or jail terms for offences like pregnancy outside marriage, failure to perform Friday prayers and propagating other religions. A second phase comes into effect 12 months later, covering the offences of theft and alcohol consumption by Muslims, which will be punishable by whipping and amputations.
Capital punishment, including by stoning, will be introduced in the final phase a year later for offences including adultery, sodomy and insulting the Koran or the Prophet Mohammed.
Most of the laws will also apply to non-Muslims.
Sultan Bolkiah, 67, announced last year that he wanted to introduce a full system of Islamic law, and warned critics who took to social media that they could be prosecuted.
"It is because of our need that Allah the Almighty, in all his generosity, has created laws for us, so that we can utilise them to obtain justice," he said at the time.
The religious turn taken by the sultan contrasts with the royal family's reputation for decadent excess.
In the past, the monarchy has been deeply embarrassed by a sensational family feud between the sultan and his younger brother Jefri over the latter's alleged embezzlement of US$15 billion during his tenure as finance minister in the 1990s.
The sultan was himself caught up in a court battle in 2007, in which he was accused of backing out of a deal with Australian businessmen to splash out £4 million (HK$52.3 million) on a gold-lined miniature Koran.
The sultan had allegedly agreed to buy it as a wedding present for his third wife, a glamorous television hostess 32 years his junior.
An Australian judge ruled that the case was outside the court's jurisdiction, and that the three businessmen should instead pursue it through the legal system in Brunei - where the sultan is immune to prosecution.
Some believe the sultan has become more religious as he has grown older.
"This is true, not just for Muslims but people of all faith. They become more religious the older they grow," said Dr Chandra Muzaffar, a Muslim scholar and president of the International Movement for a Just World.
Joseph Chinyong Liow, a Singapore-based professor who specialises in Muslim politics, also said the move could indicate the sultan was becoming more conservative as he aged.
"The sultan himself is at a point where there is a need to come to terms with religious identity, both personally and for the country," he said.
Liow said the sultan might view Islamic law as a popular step, as support grows among some Muslims in Southeast Asia for a post-colonial return to Muslim roots, especially in the face of Western influences. Brunei has long implemented some sharia law, mainly for civil matters such as marriage. But last year the sultan said he wanted to introduce a full set of Islamic laws to guard against the "challenges" of globalisation, including the impact of the internet.
Muslim ethnic Malays, who make up about 70 per cent of the population, are broadly supportive of the move by their revered father-figure. But some Malays and non-Muslim citizens privately express unease. About 15 per cent of Brunei's people are non-Muslim ethnic Chinese.
Britain granted independence to Brunei in 1984 but has maintained a close relationship ever since.
A 1,000-strong regiment of the British Army, the Royal Gurkha Rifles, has been located there since the late 1950s and is paid for by the sultan.
In March, Britain's Ministry of Defence said it was in discussions with the authorities in Brunei to clarify whether the new laws would have any impact on the British troops.
Last Wednesday, a ministry spokeswoman said she was unable to comment on the outcome of the talks.
Muzaffar viewed the implementation of hudud as "disturbing", saying that being a Muslim had been reduced to meting out punishment, instead of alleviating poverty and striving for justice and transparency.
"Being Islamic has been reduced to being committed to implementing a penal code. Greater accountability, greater ethics in public life, surely that's also being spiritual," Muzaffar said.
"He [the sultan] should be working towards a constitutional monarchy. He should think of a more sustainable political system, that is answerable to the people. That is being Islamic."
Additional reporting by Agence France-Presse