With the death of his mother Queen Elizabeth on Thursday, Prince Charles has finally become king of the United Kingdom and 14 other realms, ending a wait of more than 70 years - the longest by an heir in British history.
The role will be daunting. His late mother was overwhelmingly popular and respected, but she leaves a royal family that has seen reputations tarnished and relationships strained, including over lingering allegations of racism against Buckingham Palace officials.
Charles confronts those challenges at the age of 73, the oldest monarch to take the throne in a lineage that dates back 1,000 years, with his second wife Camilla, who still divides public opinion, by his side.
To detractors, the new king is weak, vain, interfering, and ill-equipped for the role of sovereign.
He has been ridiculed for talking to plants and obsessing over architecture and the environment, and will long be associated with his failed first marriage to the late Princess Diana.
Supporters say that is a distortion of the good work he does, that he is simply misunderstood and that in areas such as climate change he has been ahead of his time.
They argue he is thoughtful and concerned about his fellow Britons from all communities and walks of life. His Prince's Trust charity has helped more than one million unemployed and disadvantaged young people since its launch almost 50 years ago.
"The trouble is you are in a no-win situation. If you do absolutely nothing at all ... they are going to complain about that," Charles once told a TV documentary. "If you try and get stuck in, do something to help, they also complain."
Throughout his life, Charles has been caught between a modernising monarchy, trying to find its place in a fast-changing and more egalitarian society, while maintaining traditions that give the institution its allure.
That tension can be seen through the lives of his own sons.
The eldest, William, 40, now the heir himself, leads a life of traditional duty, charity work and military pageantry.
Younger son Harry, 37, resides outside Los Angeles with his American ex-actress wife Meghan and family, forging a new career more in keeping with Hollywood than Buckingham Palace.
The brothers, once very close, are now barely on speaking terms.
Groomed from birth to be king one day, Charles Philip Arthur George was born at Buckingham Palace on Nov. 14, 1948, in the 12th year of the reign of his grandfather, King George VI.
Just 3 when he became heir apparent after his mother became queen in 1952, Charles's upbringing was always different from previous future monarchs.
Unlike predecessors educated by private tutors, Charles went to Hill House school in West London before becoming a boarder at Cheam School in Berkshire, which was attended by his father Prince Philip and where he was later head boy.
He was then sent to Gordonstoun, a tough boarding school in Scotland where Philip had also studied. He described his time there as hell: he was lonely and bullied. "A prison sentence," he reportedly said. "Colditz with kilts."
Breaking with tradition again, he went to Trinity College, Cambridge, to study archaeology and physical and social anthropology but later changed to history.
During his studies he was formally crowned Prince of Wales, the title traditionally held by the heir to the throne, at a grand ceremony in 1969, having spent nine weeks at a Welsh university where he said he faced almost daily protests from nationalists.
The following year he became the first British heir to receive a degree.
Like many royals before him, he joined the armed forces, initially with the Royal Air Force in 1971 and later with the Navy, rising through the ranks to command the minesweeper HMS Bronington, before ending active service in 1976.
As a young prince, he cut a dashing, sporty figure who loved skiing, surfing, and scuba diving. He was a keen polo player and also rode as a jockey in a number of competitive races.
In 1979, his great-uncle Lord Mountbatten, who he described as "the grandfather I never had", was killed in an Irish Republican Army (IRA) bombing, a loss that deeply affected him.
"It seemed as if the foundation of all that we held dear in life had been torn apart irreparably," he later said.
On leaving the Navy in 1976 he searched for a role in public life as there was no clear constitutional job for the heir, saying he had to "make it up as you go along".
"That's what makes it so interesting, challenging and of course complicated," he said of his role in a documentary to mark his 70th birthday.