US president Barack Obama has led the tributes from leaders around the world in response to the death of Baroness Thatcher, who has died at the age of 87 after suffering a stroke.
Mr Obama described Lady Thatcher as a "true friend" to the US. In a statement, he said: "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."
Former US president Bill Clinton said America had lost "one of its dearest friends and most valued allies".
He said: "Lady Thatcher understood that the special relationship which has long united our two nations is an indispensable foundation for peace and prosperity. Our strong partnership today is part of her legacy.
"Hillary, Chelsea, and I extend our condolences to her family and to the people of the United Kingdom."
Clinton's predecessor, George HW Bush, who was in power in the last few years of Mrs Thatcher's administration, issued a statement, which said: "Margaret was, to be sure, one of the 20th century's fiercest advocates of freedom and free markets – a leader of rare character who carried high the banner of her convictions, and whose principles in the end helped shape a better, freer world.
"May God bless the memory of Margaret Thatcher."
Reformist Soviet leader Mikhail Gorbachev described the former prime minister as a "heavyweight politician".
"Margaret Thatcher was a heavyweight politician and a striking person. She will remain in our memories, and in history," he said.
Irish Taoiseach Enda Kenny described Mrs Thatcher as a formidable leader.
"Mrs Thatcher was a formidable political leader who had a significant impact on British, European and world politics. During her 11 years as prime minister, she defined an era in British public life," he said.
"While her period of office came at a challenging time for British-Irish relations, when the violent conflict in Northern Ireland was at its peak, Mrs Thatcher signed the Anglo-Irish Agreement which laid the foundation for improved North-South cooperation and ultimately the Good Friday Agreement."
Lech Walesa, the Polish anti-communist politician who led the Solidarity movement and was his country's first president after communism, hailed Baroness Thatcher as a "great person", it was reported.
He said: "She did a great deal for the world, along with Ronald Reagan, Pope John Paul II and Solidarity, she contributed to the demise of communism in Poland and Central Europe."
Another prominent figure in the fight against communism in Europe, Vaclav Klaus, said her name will always remain important.
In a statement on his website, the former Czech president, who entered politics during the country's Velvet Revolution, said her death "is for all supporters of freedom, democracy, market capitalism and a huge loss.
"She was one of the most prominent political figures last quarter of the 20th century, and I believe that the passage of time, her name will not lose its importance," he said.
South African's ruling African National Congress party expressed its sadness at Baroness Thatcher's death, despite being on the "receiving end" of her policies.
In a statement on their website, the party said: "The African National Congress has learnt with sadness of the passing of Mrs Margaret Thatcher, the former prime minister of Britain at the age of 87."
The statement went on: "The ANC was on the receiving end of her policy in terms of refusing to recognise the ANC as the representatives of South Africans and her failure to isolate Apartheid after it had been described as a crime against humanity, however we acknowledge that she was one of the strong leaders in Britain and Europe to an extent that some of her policies dominate discourse in the public service structures of the world.
"Long after her passing on, her impact will still be felt and her views a subject of discussion.
"The ANC extends its condolences to her family, her loved ones and the people of Britain. May her soul rest in peace."
German Chancellor Angela Merkel reportedly praised her actions in helping to bring about the end of the Cold War.
"As a long-serving prime minister, she shaped modern Britain as few have before or since," she said.
"She was one of the greatest leaders in world politics of her time.. I will never forget her contribution in overcoming Europe's partition and the end of the Cold War.
"Margaret Thatcher was not a feminist but by proving herself as a woman in the highest democratic post when this was far from usual, she gave an example to many. My thoughts and sympathy are with her children."