Margaret Thatcher, the first female prime minister of Britain and a giant of 20th century conservatism, is dead at the age of 87.

A spokesperson confirmed that Thatcher died Monday following a stroke.

"It is with great sadness that Mark and Carol Thatcher announced that their mother Baroness Thatcher died peacefully following a stroke this morning," said Thatcher's spokesperson Lord Timothy Bell. "A further statement will be made later."

Tributes quickly began to pour in for Thatcher, who served as Prime Minister of Britain from 1979 to 1990 and ushered in an age of Conservatism that earned her the nickname “The Iron Lady.”

British Prime Minister David Cameron tweeted his condolences Monday: "It was with great sadness that I learned of Lady Thatcher's death. We have lost a great leader, a great Prime Minister, and a great Briton," he wrote.

Canadian Prime Minister Stephen Harper also mourned Thatcher's death, saying "the world has lost a giant among leaders."

“While many in positions of power are defined by the times in which they govern, Margaret Thatcher had that rarest of abilities to herself personify and define the age in which she served. Indeed, with the success of her economic policies, she defined contemporary conservatism itself," Harper said in a statement.

"I recall with pride her eloquent portrayal of the philosophical groundings of the principles that have -- and I hope forever will -- unite the British and Canadian peoples."

Former Canadian prime minister Brian Mulroney, who came to know Thatcher well during his time in office, called her "an enormous power."

"She's a wonderful person, a delightful person, a highly principled woman and a very talented leader -- not always easy to get along with because she could be very tough with everybody, but I admired her enormously," Mulroney told CTV's Canada AM on Monday.

Mulroney added that Thatcher was always the best-prepared person at any meeting, "looked like a million bucks" and typically had the smallest political entourage with just one or two aides at her side.

Thatcher’s legacy

Thatcher's time in office was marked by her willingness to take on controversial, politically thorny challenges.

She pushed for the privatization of state industries, often struggling against labour unions to pursue her radical free-market philosophy.

Her ideology and policies are now immortalized in the term “Thatcherism,” which also applies to a brand of Conservatism driven by conviction, not consensus of opinion.

Thatcher’s famously strong iron will was tested many times during her leadership. The first came soon after her election, when IRA prisoners went on a hunger strike, demanding concessions from the British government. Thatcher refused to negotiate and 10 prisoners died.

In 1982, she retaliated against Argentina after that country invaded the Falkland Islands. It took 74 days for the British to regain control. Hundreds of Argentines were killed, along with 255 British personnel.

“Rejoice at that news, and congratulate our forces and the marines,” Thatcher said.

In one of her rare political retreats, she backed away from a proposed nation-wide poll tax, or community tax, after it sparked massive public protest and rioting.

In 1990, it was her strong will that cost her the leadership of the Conservatives. Despite protests from other Tory ministers, she refused to budge on Britain’s involvement with the European Union. Michael Heseltine challenged her leadership, and Thatcher was forced to resign when it became obvious she had lost the confidence of her party.

“I am leaving for Downing street for the last time,” a visibly sad Thatcher told reporters.

Britain’s first female leader

At the time of her election, there were just 27 female MPs. When she left office 11 years later that number had grown to 43.

Baroness Shirley Williams, who met Thatcher when she was a Labour cabinet minister in the 1970s, told the BBC that Thatcher succeeded as a female politician through sheer determination. Although, becoming prime minister had not been her immediate goal.

"She had this extraordinary power of the will: single minded, with a clear objective and it was not to be the first woman prime minister,” Williams said. “It was quite straight-forwardly to be leader of the Conservative Party.”

Some ministers feel that Thatcher could have done far more for other female politicians, especially considering that there was just one other female cabinet minister during her leadership.

"Margaret Thatcher broke through the glass ceiling in politics,” Patricia Hewitt, a Labour minister, told the BBC. “But it is a tragedy that, having become the U.K.'s first woman prime minister, she did so much to undermine the position of women in society.”

Thatcher's health has failed in recent years, and her death does not come as a shock in the U.K., said CTV's former London bureau chief Tom Kennedy. However, he said the news will come as a tough blow to many.

"She's an extraordinary woman in that she came from a working-class background, was the daughter of a green grocer. She became very interested in politics at a young age, tried on a couple of occasions to get elected to the house of commons and failed, and then finally made a breakthrough and she quickly rose to the top of the conservative party and then became prime minister," Kennedy told CTV News Channel from London.

"She really was a political giant in this country and represented a breakthrough for women in power here as well. So I think there will be a period of mourning here now that she has died."

Thatcher had been hit with tragedy within her own family in the past decade. Her husband, Sir Denis, passed away in 2003. He was a 64-year-old retired oil executive when Thatcher became prime minister, and was frequently at her side.

Thatcher’s son Sir Mark was arrested in South Africa after pleading guilty to unwittingly bankrolling a failed coup in Equatorial Guinea. He was given a four-year suspended sentence, and was able to appear at Thatcher’s 80th birthday celebration with his twin sister Carol.

Thatcher retired from public life in 2002 following a stroke. She has suffered several strokes since then and struggled with dementia.