By Peter Hunt
BBC royal correspondent
She has a public persona that we are all familiar with and a jealously guarded private personality.
Those who are admitted into what has been called by one author "the golden circle" rarely shed much light on the Queen they meet at ease.
To do so, could result in exclusion from the next intimate royal luncheon or shooting party.
The rest of us are offered scraps from the Windsor table.
We hear, for example, that our monarch has a good sense of humour and is an effective mimic.
These morsels aside, it is little wonder then that the woman who adorns our stamps is often referred to as an "enigma".
Margaret Rhodes, the Queen's cousin, recalls an idyllic childhood playing with Princess Elizabeth and Princess Margaret.
"When they were very small, it was mostly playing at being horses.
"We were circus horses, or riding ponies or anything you like, but it involved a lot of neighing, cantering and galloping."
That easy way of life changed with the abdication crisis in 1936.
Sonia Berry remembers how once her "greatest friend" had become heir to the throne, she had to curtsy to her and call her Princess.
All those who have known the Queen since she was a child talk of her slightly serious nature, especially when compared with her younger sister.
There have been moments when she could escape the rigid formality of Palace life.
VE Day in 1945 was such an occasion.
Together with Jean Woodroffe, one of her first ever ladies in waiting, the young princess slipped, unnoticed out of Buckingham Palace to join the millions thronging the streets of London.
Their experience remains a vivid memory for Mrs Woodroffe.
"What was amusing is that we went into the Ritz hotel through one door and out of the other door, the other end, doing the conga.
"And the extraordinary thing was that nobody seemed to take much notice.
"And then we stood outside Buckingham Palace with the crowd and we all shouted, 'We want the King' with everybody else, until the King and Queen came out onto the balcony."
The carefree princess doing the conga was the briefest of moments.
Destiny called in 1952 when she was just 25.
Prince Charles never felt he had his parents' approval, Mr Turner says
Her reign has been examined in considerable detail.
The highs - her duty and consistency, and the lows - the marital break-ups, her annus horribilis and the initial royal reaction to Diana's death.
One former senior aide has said recently that the family learnt a tough lesson that week in 1997 about "public" grief and the need to communicate sorrow.
What is striking about the Queen's long life is how muted the criticism has always been.
Even republicans accept they will have to bide their time.
Much has been written about her family's traumas.
Graham Turner, a respected royal author, believes she is a very remarkable monarch who has been an icon of steadiness and good behaviour.
The Queen has been blamed for her children's travails
However, it is on the domestic front where he believes she can be found wanting.
He argues that together with Prince Philip she shares some of the blame for her children's travails.
In Mr Turner's view, Prince Charles never felt he had his parents' approval.
Friends and supporters of the Queen insist that the crucial relationship between the heir and the monarch has improved.
One of those who knows the Queen well, argues that the gulf has been hugely exaggerated.
They are disparate characters, he says, but there is affection there.
This landmark occasion will inevitably prompt speculation in some quarters about the Queen's longer term intentions.
The Queen turns 80 on Friday
To put it bluntly, will she ever retire?
All the indications, at the moment are that abdication is not on the cards.
It traumatised her parents and the nation in the 1930s and it undermines the principles of a hereditary monarchy.
And it is for that same reason that the idea of "skipping a generation" with Prince William inheriting the throne is unlikely to find favour in Palace circles.
However, it is a vivid reminder of just how bad things were in the 1990s, that officials did at least contemplate such a scenario before rejecting it.
Abdication might be off the agenda but the status quo is likely to be gently tinkered with - 80-year-olds, however fit, cannot be charging around the place.
The Queen is likely to continue doing the "big" occasions.
Destiny called in 1952 when the Queen was just 25
Her son, and other children, will - as they do already - take on some of the other tasks.
For the Queen, her birthday is an occasion to celebrate with no obvious clouds on the horizon.
The problems of the past suddenly seem a distant memory.
The Royal Family appears to be in calmer waters.
As one who knows her remarked dryly, "she is outrageously popular and approaching sainthood".
Queen Elizabeth II, according to her cousin, Margaret Rhodes, has blossomed in recent years.
"I think in a funny way, perhaps, the death of Queen Elizabeth the Queen Mother had quite a huge effect on the Queen.
"Not only of sadness, but in a way that she could come into her own as the head of the family and as the most senior royal lady".
Mrs Rhodes is voicing the views of many of those who have known the monarch down the decades when she says: "The Queen will continue to do as much as she can, as she always has done, until she drops."