Baroness Thatcher, who was Britain's prime minister for over a decade, has died today aged 87 after suffering a stroke, her family said.
The ex-premier is to have a funeral at St Paul's Cathedral with full military honours in recognition of her influence in the UK.
Tributes were paid to Lady Thatcher, with the Queen said to be "sad" at the news of the death, while Prime Minister David Cameron called her a "great leader" and a "great Briton".
Former Labour Prime Minister Tony Blair said Lady Thatcher was "a towering political figure" who had a vast global impact.
– Tony Blair
Margaret Thatcher was a towering political figure.
Very few leaders get to change not only the political landscape of their country but of the world. Margaret was such a leader. Her global impact was vast.
And some of the changes she made in Britain were, in certain respects at least, retained by the 1997 Labour Government, and came to be implemented by governments around the world.
As a person she was kind and generous spirited and was always immensely supportive to me as Prime Minister although we came from opposite sides of politics.
Even if you disagreed with her as I did on certain issues and occasionally strongly, you could not disrespect her character or her contribution to Britain’s national life.
She will be sadly missed.
Current Labour leader Ed Miliband said she had "moved the centre ground of British politics" and called her "an extraordinary politician and unique political figure."
Sir John Major told ITV News that his predecessor was the "right politician for the time" and said "she had a clear view of what was necessary."
Global leaders also paid tribute to the Iron Lady, with US President Barack Obama calling her a "true friend" to the US.
– US President Barack Obama
With the passing of Baroness Margaret Thatcher, the world has lost one of the great champions of freedom and liberty, and America has lost a true friend.
As a grocer’s daughter who rose to become Britain’s first female prime minister, she stands as an example to our daughters that there is no glass ceiling that can’t be shattered.
As prime minister, she helped restore the confidence and pride that has always been the hallmark of Britain at its best.
And as an unapologetic supporter of our transatlantic alliance, she knew that with strength and resolve we could win the Cold War and extend freedom’s promise.
Here in America, many of us will never forget her standing shoulder to shoulder with President Reagan, reminding the world that we are not simply carried along by the currents of history—we can shape them with moral conviction, unyielding courage and iron will.
Michelle and I send our thoughts to the Thatcher family and all the British people as we carry on the work to which she dedicated her life—free peoples standing together, determined to write our own destiny.
Reformist Soviet leader Mikhail Gorbachev described the former prime minister as a "heavyweight politician", while Nancy Reagan, the wife of former US President Ronald, said the world owed Lady Thatcher "a debt of gratitude."
The former Tory leader was also widely condemned by those on the Left, with ex-London Mayor and Labour MP Ken Livingstone criticising her legacy.
– KEN LIVINGSTONE ON SKY NEWS
She created today's housing crisis, she produced the banking crisis, she created the benefits crisis ... Every real problem we face today is the legacy of the fact she was fundamentally wrong.
Singer Morrissey said Lady Thatcher was "a terror without an atom of humanity" and that "she destroyed the British manufacturing industry, she hated the miners, she hated the arts, she hated the Irish Freedom Fighters and allowed them to die".
Sinn Fein leader Gerry Adams also criticised Lady Thatcher, saying "her Irish policy failed miserably":
– Sinn Fein leader Gerry Adams
Margaret Thatcher did great hurt to the Irish and British people during her time as British Prime Minister.
Working class communities were devastated in Britain because of her policies.
Lady Thatcher became the first female prime minister when she was elected in 1979 and spent 11 years in Downing Street.
The former Tory leader's impact was underlined by the reaction to her death at the Ritz Hotel in London this morning, where she suffered a stroke while recuperating following a minor operation.
ITV News' Bill Neely reports:
Mr Cameron cut short an official trip to Europe and announced that Parliament was being recalled from its Easter recess on Wednesday to give MPs the chance to pay tribute.
Both Labour and the Tories suspended campaigning ahead of next month's local elections and flags at Westminster and Buckingham Palace were flying at half-mast.
As Lady Thatcher's health deteriorated, the issue on whether she should be granted a state funeral - as Sir Winston Churchill was - grew increasingly controversial.
However, it emerged that she rejected that idea and also insisted she did not want her body to lie in state or money to be spent on a fly-past.
Next week the streets will be cleared for a procession from Westminster to St Paul's, where there will be a televised service attended by dignitaries from around the world. The day has yet to be confirmed.
Lady Thatcher's frail condition - especially after the death of husband, Denis, in 2003 - led to frequent bouts of speculation about her health.
However, friends who saw her regularly said she remained alert and interested in politics until recently.
She was said to be delighted Mr Cameron, and before him, Gordon Brown extended invitations to visit 10 Downing Street and Chequers.
The Thatcher family have asked well-wishers to donate to the Royal Hospital Chelsea instead of leaving flowers.
But a solitary yellow daffodil was placed at the feet of Lady Thatcher's statue outside the Commons chamber today.