Tributes -- and some criticism -- flooded in Monday from around the world.
U.S. President Barack Obama said the world had "lost one of the great champions of freedom and liberty" and the United States had 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," he said.
U.S. Secretary of State John Kerry said the world had "lost a transformative leader who broke the glass ceiling in global politics" and "defined grit on the world stage."
"Margaret Thatcher took a country that was on its knees and made Britain stand tall again," said Cameron, who leads today's Conservative Party. He also described her as a "patriot prime minister" with a "lion-hearted love" for her country.
Former British Prime Minister Tony Blair, who led the opposition Labour Party in government from 1997 to 2007, said Thatcher was a "towering political figure" who would be greatly missed.
"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," he said.
Former U.S. President George H.W. Bush -- whose first years in the White House overlapped with the end of Thatcher's time as prime minister, but who served as vice president at the height of her power and influence -- called her one of the "fiercest advocates of freedom and free markets."
And former U.S. Secretary of State Henry Kissinger told CNN that Thatcher was a "tremendous prime minister" and a "great lady."
But Northern Ireland politician and Sinn Fein leader Gerry Adams gave a very different view of Thatcher's legacy.
"Margaret Thatcher did great hurt to the Irish and British people during her time as British prime minister," he said. "Working class communities were devastated in Britain because of her policies."
She will be remembered in particular for "her shameful role during the epic hunger strikes of 1980 and 81" in Northern Ireland, and her Irish policy "failed miserably," he concluded.
South Africa's governing African National Congress recognized Thatcher's enduring influence but pointed out that she got it wrong on apartheid. Thatcher infamously dismissed Nelson Mandela's ANC as a terrorist organization.
The party "was on the receiving end of her policy in terms of refusing to recognize the ANC as the representatives of South Africans, and her failure to isolate apartheid after it had been described as a crime against humanity," the ANC statement said. "However we acknowledge that she was one of the strong leaders in Britain and Europe."
'A great destroyer'
Officials in the Falkland Islands said they would never forget Thatcher's decision to defend the South Atlantic territory in 1982.
"Her friendship and support will be sorely missed, and we will always be thankful for all that she did for us," said Mike Summers of the Falkland Islands Legislative Assembly.
The United Kingdom and Argentina went to war over the territory in 1982 after the then-military government in Argentina landed troops on the islands. Argentina put its death toll from the conflict at around 645. Britain says its civil and military losses amounted to 255.
Over the past year or more, rhetoric between the two countries over the islands has escalated sharply, and Argentina's state-run Telam news agency offered an unflinching look Monday at the South American country's take on Thatcher's legacy.
Articles described her as "a symbol of war," "an expression of inequality" and "a great destroyer."
For British filmmaker Ken Loach, known for his gritty social critiques, Thatcher was "the most divisive and destructive prime minister of modern times."
"Mass unemployment, factory closures, communities destroyed -- this is her legacy. She was a fighter and her enemy was the British working class," he said.
"Her victories were aided by the politically corrupt leaders of the Labour Party and of many trades unions. It is because of policies begun by her that we are in this mess today."
Her final years
Thatcher was ultimately brought down, not by British voters, but by her own Conservative Party.