Thailand's King Vajiralongkorn - his name means "adorned with jewels or thunderbolts" - was born on 28 July 1952, the first son and second child of Queen Sirikit and King Bhumibol Adulyadej, who had succeeded to the throne unexpectedly six years previously.
After decades of uncertainty over royal succession, the birth of a male heir was seen as vital for the monarchy, at a time when its primacy in Thailand's political hierarchy was uncertain. The absolute monarchy had been overthrown in 1932, followed by an abdication in 1935, and 11 years in which the country had no sitting king.
In King Vajiralongkorn's early years he was educated at a palace school in Bangkok. At the age of 13 he was sent to two private schools in the UK for five years, and then for a final year at a school in Sydney, Australia. He spent the following four years being trained at the Royal Military College, Duntroon, in Canberra.
By his own account, he struggled to keep up at school, blaming his pampered upbringing in the palace. He also found it hard to make the grade at Duntroon.
He continued to receive advanced military training in Thailand, the UK, US and Australia, and became an officer in the Thai armed forces. He is a qualified civilian and fighter pilot, flying his own Boeing 737 when he travels overseas.
He was formally given the title of Crown Prince by his father in an investiture ceremony in 1972, making him the official heir. But by that time questions were being raised about his fitness to succeed to the throne.
He showed none of the enthusiasm of his younger sister Princess Sirindhorn for his father's development projects and there were persistent rumours of womanising, gambling and illegal businesses.
In 1981 his mother, Queen Sirikit, alluded to these problems, describing her son as "a bit of a Don Juan" and suggesting that he preferred spending his weekends with beautiful women rather than performing duties.
In a rare audience with Thai journalists in 1992, he denied the rumours that he was involved with mafia-like figures and underworld businesses.
In 1977 he married his cousin Princess Soamsawali and they had their first child, Princess Bajarakitiyabha, in December 1978. However, by then he was involved with a young actress, Yuvadhida, with whom he had five children from 1979 to 1987. He married her in 1994, but in 1996 very publicly denounced her and disowned his four sons, who were studying in the UK.
He married his third wife Srirasmi, a lady-in-waiting, in 2001, and had another son, Prince Dipangkorn, with her in 2005.
In 2014 Srirasmi was stripped of her royal title and nine of her relatives, including her parents, were arrested for lese majeste on charges they had abused their connections with the Crown Prince. A police officer linked to the family died in custody after falling from a window.
That charge, of abusing his name, has also been made against others who became close to the Crown Prince, notably a well known fortune teller who, together with another police officer, died after being arrested in 2015. At the same time, the Crown Prince's personal bodyguard was stripped of his rank for "disobeying royal commands" and "threatening the monarchy by pursuing his own interests". He disappeared and is believed to have died.
For years he has been seen in the company of a former Thai Airways flight attendant, Suthida, who was made an officer of the Royal Household Guard, with the rank of Lieutenant-General. He also famously promoted his pet poodle Fu-Fu to the rank of Air Chief Marshall.
In May 2019, days before his coronation, King Vajiralongkorn married her and the palace announced that she was to become Queen Suthida and will hold royal title and status as part of the royal family.
The severity of the lese majeste law has prevented any open discussion of the new king's suitability inside Thailand. But privately, the possibility of Vajiralongkorn being passed over for his more popular and dutiful sister Sirindhorn was often talked about, encouraged by her own royal title being elevated in 1978 and by a change in palace succession law to allow a female to succeed to the throne.
But that is only possible where there is no male heir, and King Bhumibol never supported the option of an alternative to his son.
As King Bhumibol's health declined, Crown Prince Vajiralongkorn began to be seen more often in public, performing traditional royal rituals on behalf of his father.
In the past there were rumours of a business relationship between him and former Prime Minister Thaksin Shinawatra, the telecoms tycoon whose party has won every election since 2001 and who was seen as a threat by much of the conservative royalist elite.
But after the coup in 2014, which deposed the government of Thaksin's sister Yingluck, the new military rulers appeared to work with the Crown Prince to ensure his succession, helping organise events like mass bicycle rides in which he and his daughters participated, presenting a less formal image of the future king to the public.
Just what kind of king Vajiralongkorn will make is hard to guess.
Although a constitutional monarch, he will wield considerable power - for example, it is almost impossible for anyone in Thailand to reject the express wishes of the monarch.
He also has a decisive say over the Crown Property Bureau, by far the wealthiest institution in Thailand, with assets valued at between $30-40bn (£24-32bn), giving the palace largely untaxed annual income of around $300m. And he commands his own personal regiment of the Royal Guard, comprising an estimated 5,000 troops.
One advantage he will not have is the immense prestige and respect built by his father over 70 years on the throne, which Thai royal experts point out must be earned, not inherited. Vajiralongkorn, at the age of 66, will not have so long to make his mark on the monarchy. But he has had decades to observe and learn from the complex flow of power that surrounds the monarch.
He presided over the elaborate and prolonged funeral rituals for the late king, giving him a chance to enhance his own standing in the process.
He may well be able to rely on the lasting reverence for his father to shore up the monarchy's central role in Thai society.