Global and political leaders across the world remembered former British prime minister Margaret Thatcher, who died on Monday, as a leader who altered the U.K.’s political and economic landscape and shaped global relations, even as she sharply divided opinion.

Tributes poured in from past and present leaders including U.S. President Barack Obama, former president George W. Bush and former Soviet leader Mikhail Gorbachev, as well as British political leaders and Queen Elizabeth II. While many praised her strength of character and hailed her achievements, some detractors said her policies had been damaging to the U.K.

The reaction followed the announcement on Monday morning of the death of Mrs. Thatcher, aged 87. “It is with great sadness that Mark and Carol Thatcher announced that their mother Baroness Thatcher died peacefully following a stroke this morning,” said Mrs. Thatcher’s spokesman, Timothy Bell.

Mrs. Thatcher took office in 1979, becoming the U.K.’s first and only female prime minister, and remained there until 1990. Her championing of free-market economics and individual choice transformed Britain’s economy and she played a role in the end of the Cold War.

“America has lost a true friend,” Mr. Obama said. “Here in America, many of us will never forget her standing shoulder to shoulder with President [Ronald] 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.”

Former Soviet leader Mikhail Gorbachev, with whom Mrs. Thatcher formed a close relationship, said in a statement on the Gorbachev Foundation’s website: “Thatcher was a politician whose words carried big weight.”

“Our first meeting in 1984 laid ground to the relationship that was at times complex, but always even and on both sides serious and responsible,” Mr. Gorbachev said. “In the end we managed to achieve mutual understanding, and this was a contribution to the changing atmosphere between our country and the West, and to the end of the Cold War,” he said.

David Cameron, the U.K.’s current prime minister and leader of Mrs. Thatcher’s Conservative Party, said: “We’ve lost a great prime minister, a great leader, a great Briton.” Mr. Cameron, who cut short a Europe trip to return to the U.K. on Monday afternoon, added: “She saved our country and I believe she will go down as the greatest British peacetime prime minister.”

But Mrs. Thatcher was a hugely divisive figure in British politics, with her detractors criticizing everything from her economic policy to approach to Europe.

“Margaret Thatcher did great hurt to the Irish and British people during her time as British prime minister,” said Irish politician Gerry Adams, president of the Sinn Fein party. “Working-class communities were devastated in Britain because of her policies.”

Mr. Adams called her role in international affairs “equally belligerent,” saying she supported Chilean dictator Augusto Pinochet and opposed sanctions against apartheid South Africa. And, in Ireland, “her espousal of old draconian militaristic policies prolonged the war and caused great suffering,” Mr. Adams said.

Irish Prime Minister Enda Kenny said Mrs. Thatcher was “a formidable political leader who had a significant impact on British, European and world politics.”

“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.”

In the U.K., the head of the main opposition Labour Party, Ed Miliband, said his party disagreed with much of what she did and that “she will always remain a controversial figure.” But he added, “We can disagree and also greatly respect her political achievements and her personal strength.”

“She will be remembered as a unique figure. She reshaped the politics of a whole generation,” Mr. Miliband added.

Nick Clegg, the deputy prime minister and leader of the Liberal Democrats, called Mrs. Thatcher “one of the defining figures in modern British politics.” He added, “Whatever side of the political debate you stand on, no one can deny that as prime minister she left a unique and lasting imprint on the country she served. She may have divided opinion during her time in politics but everyone will be united today in acknowledging the strength of her personality and the radicalism of her politics.”

Queen Elizabeth was “sad to hear the news of the death of Baroness Thatcher,” a spokesman for the British monarch said. “Her majesty will be sending a private message of sympathy to the family.”

Mrs. Thatcher’s funeral service will be held at London’s St. Paul’s Cathedral, which will be followed by a private cremation.

[Wall Street Journal]