The Queen’s life has been defined by her dedication to duty and strong belief in her role as the nation’s monarch.
Stoical, pragmatic and private, and with an unshakeable Christian faith, she is one of the most famous figures on the planet.
But little is known about the real woman behind the crown. To some she is seen as remote and less approachable than other European royals while others believe she is a great British institution and deserves respect.
A strong sense of humour is one quality we do know she possesses and she uses it to put everyone from presidents to the public at ease if they are apprehensive about meeting the 5ft 4ins monarch.
As head of state, the armed forces and the Church of England, the Queen is at the centre of national life but she is also a wife with more than 65 years of marriage under her belt, a mother, grandmother and great-grandmother.
Away from the trappings of state, her love of horses, racing and her corgis, the short-legged dogs which mill around Buckingham Palace, have been her lifelong interests.
Princess Elizabeth Alexandra Mary was born at 2.40am on April 21, 1926, at 17 Bruton Street in Mayfair in the year of the General Strike.
Fair-haired and blue-eyed, she was the first child of the Duke of York, the second eldest son of King George V and Queen Mary, and his wife the Duchess.
The abdication of her uncle, Edward VIII, in 1936 changed everything, leaving her father to become king and making the then Princess Elizabeth the heir presumptive.
Looking forward to her destiny, she pledged to serve the Commonwealth in a radio broadcast made in 1947: “I declare before you all that my whole life, whether it be long or short, shall be devoted to your service and the service of our great imperial family to which we all belong.”
The Queen first met her dashing blond-haired, blue-eyed, distant cousin Prince Philip of Greece in the mid-1930s and they wrote to each other while the future consort was at sea during the Second World War.
They married at Westminster Abbey on November 20, 1947 and lived in Malta for a time while the Duke of Edinburgh was on naval service, giving them their only real taste of life as a relatively ordinary couple.
With their two young children, Prince Charles, born in 1948, and Princess Anne, born in 1950, they had a brief idyllic existence on the Mediterranean island.
The success of their long-lasting marriage has been put down to their compatibility of character, with the Queen seen as passive, cautious and conventional while the Duke is more adventurous, tempestuous and active.
Elizabeth and Philip had been married for less than five years when their lives altered irrevocably following the death of the King on February 6, 1952.
The Queen’s Coronation a year later on June 2 captured the hearts and minds of a nation starved of pageantry by the war.
Her third child, Prince Andrew, was born in 1960, and her fourth, Prince Edward, arrived in 1964.
In 1977, record crowds greeted her during her Silver Jubilee celebrations and thousands held street parties in her honour.
The Queen is known to favour simplicity in court life and takes a serious and informed interest in government business, aside from her ceremonial duties.
She also attaches great importance to her role as head of the Commonwealth.
But the private lives of her family, so often played out on a public stage, will have been a source of concern for her over the decades.
The Queen dubbed 1992 her “annus horribilis” as during that year the Princess Royal divorced, the Duke and Duchess of York separated, the Prince and Princess of Wales were splitting up and Windsor Castle went up in flames.
Five years later the Queen and the monarchy faced one of its gravest crises when Diana was killed in a Paris car crash in 1997. She was perceived as out of step with the feelings of mourners wondering why the Queen, who was at Balmoral with Princes William and Harry, took so long to speak publicly about the tragedy.
In 2002, the Queen suffered the tragic double blow of losing both the Queen Mother and her sister, Princess Margaret, within weeks of one another.
It was her Golden Jubilee year but the celebrations continued and were a resounding success, with one million people turning out to party in June on the streets of London, much like her Diamond Jubilee 10 years later.
The new millennium has been a much happier period for the Queen, with Charles marrying his long-term love Camilla, now the Duchess of Cornwall, in 2005.
The Duke and Duchess of Cambridge married in 2011 and now have two children, future monarch Prince George and Princess Charlotte.
The Queen became Britain’s longest-reigning monarch on September 9 last year – passing her great-great grandmother Queen Victoria’s record.
The milestone is likely to set the seal on her reign as sovereign, which so far has lasted more than 64 years.
As she approaches her 90th birthday, the Queen, with her familiar look of a brimmed hat, grey curled hair, brightly coloured coats and pristine white gloves, looks set to reign on.