As the more sensible, older brother to Prince Harry, he relies on a circle of close, trusted friends and still regards the media with suspicion.
The Prince's childhood was marked by the bitter breakdown of his parents' marriage while he was a student at Eton and then, in 1997, the death of his mother in a car crash.
The 15-year-old and his brother, who was just 12, were watched by millions around the world as they walked behind their mother's cortege at her funeral in front of vast crowds of mourners.
Prince William Arthur Philip Louis of Wales was born at 9.03pm on June 21, 1982, at St Mary's Hospital, Paddington in London, weighing 7lb 1 1/2oz.
The Princess became pregnant just four months after her fairytale wedding to the Prince of Wales.
He wrote to a friend after his first son was born: ''He really does look surprisingly appetising and has sausage fingers just like mine.''
Prince William was christened by the Archbishop of Canterbury, Dr Robert Runcie, on the Queen Mother's 82nd birthday on August 4, 1982 in the Music Room at Buckingham Palace.
As naughty as any other youngster, he sometimes played up in public - notably at the Duke of York's wedding, where he pulled faces at the bridesmaids.
He was sent to Mrs Mynor's Nursery School in west London aged three, then Wetherby School and Ludgrove School in Berkshire before attending Eton.
Early school reports showed he had a flair for spelling and was good at sports.
In 1991, he suffered a depressed skull fracture after being hit on the side of the head with a golf club by a friend at school, which has left him with a faint scar on his forehead.
As a teenager, the Prince would, like his mother once did, hide under his floppy blond fringe when confronted by photographers.
His parents' marriage crumbled amid scandal and intense press interest while William was at Eton.
Then on August 31 1997 his mother was killed suddenly in a car crash in Paris,
The Prince of Wales, who was with his sons at Balmoral, let them sleep through the night before breaking the news to them in the morning.
In the aftermath the media agreed to leave the princes alone while they finished their education, meaning news on the boys during their teen years was limited.
At Eton, William went on to gain 10 GCSEs in 1998, with three A*(star) grades, five As and two Bs, and became one of 21 prefects.
In his A-levels he gained an A in Geography, B in History of Art and a C in Biology.
After leaving school, he went on a gap year which included jungle training in Belize with the Welsh Guards and a stint with Raleigh International in Chile.
The Prince was shown tackling domestic chores - making him possibly the first future King to be pictured in rubber gloves scrubbing a toilet floor.
He began his four years at St Andrews university in Scotland in 2001, but stayed away from Freshers Week to avoid the spotlight and later struggled to adjust.
He switched from history of art to geography, got used to the isolated town and began dating flatmate Kate Middleton.
His 21st birthday - an Out of Africa themed do at Windsor Castle - caused a security scare when ''comedy terrorist'' Aaron Barschak gatecrashed the party.
During his final year, news broke that his father was to finally marry his former mistress Camilla Parker Bowles.
William, who acted as a witness on the day, supported his father's decision, knowing Camilla - now the Duchess of Cornwall - made him happy.
He gained a 2:1 in his MA and his graduation was attended by his new stepmother and the Queen.
His first solo foreign tour was to New Zealand in the summer of 2005 when he joined the British Lions to support them in their clashes against the All Blacks.
His first royal patronage was announced the same year - Centrepoint, one of his mother's favourite homelessness charities.
In December 2009, he spent a night sleeping rough on the streets of London after being challenged to do so by Centrepoint.
He is also President of the Football Association and has taken on the numerous other patronages, including Tusk Trust, the African conservation charity favoured by his friend and rumoured ex-girlfriend Jecca Craig.
The Prince has started to carry out royal engagements, but his public appearances remain limited, with his focus being on his military career.
In 2010, he embarked on his first official overseas tour to Australia and New Zealand and by the autumn of that year had graduated as a full-time RAF Search and Rescue helicopter co-pilot.
While his younger brother scuffled with a paparazzi photographer and dabbled with cannabis, the Prince stayed out of trouble in his teenage years and beyond.
When Harry wore a Nazi uniform to a fancy dress party, sensible William went as a lion.
But the royal brothers were united in remembering their mother on the 10th anniversary of her death, holding a concert and a memorial service in her honour.
Their careers initially followed similar paths with William following Harry into Sandhurst to train as an officer in the Army in 2006, and then joining his sibling's regiment, the Household Cavalry's Blues and Royal.
But William later decided to transfer his service to the Royal Air Force and became a full-time co-pilot with the RAF's Search and Rescue Force.
He faced criticism after he landed an RAF Chinook helicopter in a field at Kate's family's house in Bucklebury, Berkshire, while training.
An aviation expert branded the flight ''ridiculous and inappropriate''.
In 2006 the police inquiry into Diana, Princess of Wales's death concluded that the Paris car crash was a tragic accident.
The Princes wanted the findings to bring an end to the speculation surrounding the matter, but this did not happen until the long awaited inquest concluded in 2008 with the jury finding the Princess and her lover Dodi Fayed were both unlawfully killed.
Protective of his wife-to-be, William has been angered by the attention she was receiving from photographers, with aides saying he wanted more than anything for her to be left alone.
Now with Miss Middleton propelled into the spotlight as his
wife-to-be, William is unlikely to be able to shake off the press interest which has already shaped his life.
Prince Harry