Born Margaret Hilda Roberts, the future prime minister was the daughter of a grocer and local alderman who later became mayor of Grantham, England. The cramped apartment above her father’s corner store in which Thatcher grew up lacked running water, central heating and even an indoor toilet.

Although she planned to pursue a political career, Thatcher graduated from Oxford University in 1947 with a chemistry degree. After a stint as a research chemist for a plastics company, Thatcher worked as a food scientist at J. Lyons and Co. where she was part of a team that found a method to increase the amount of air injected into ice cream so that it could be manufactured with fewer ingredients at a lower cost. The breakthrough led to the production of soft-serve ice cream, which was dished out from trucks across Great Britain under the brand Mr. Whippy.

Thatcher, who was one of the first female presidents of the Oxford University Conservative Association, gained the notice of the Conservative Party soon after her graduation. As a 24-year-old, she was the youngest candidate to stand for a seat in the House of Commons during the election of 1950. Adopting the slogan “Vote Right to Keep What’s Left,” Thatcher faced an uphill battle in the working-class district of Dartford, which leaned toward the opposition Labour Party. Although defeated, she garnered considerable media attention and praise for cutting the Labour majority by a third. She lost in Dartford again in 1951, but she finally won a seat in Parliament after running in the staunchly Conservative district of Finchley in northern London in 1959.

After marrying wealthy, divorced businessman Denis Thatcher in 1951, Margaret gave up her scientific career. “I just didn’t like staying in the laboratory that long,” she said in a 1987 television interview. “I wanted to have more direct work to do with people.” The couple had twins Mark and Carol in 1953, and the following year Thatcher became a barrister specializing in tax law.

Before a Soviet newspaper dubbed her the “Iron Lady” following a strident anti-Communist speech she delivered in 1976, Thatcher was known by a less complimentary moniker. While serving as secretary of education in 1970, she ended a free milk program for schoolchildren between the ages of 7 and 11 in order to meet the Conservative government’s pledge to cut spending. Political opponents and the media labeled her “Thatcher, the Milk Snatcher,” and the Sun newspaper even called her “The Most Unpopular Woman in Britain.”

“There will not be a woman prime minister in my lifetime,” she told the Finchley Press in 1970. “The male population is too prejudiced.” Five years later, she supplanted former Prime Minister Edward Heath as Conservative leader, becoming the first woman to head a major British political party, and in 1979 she proved herself wrong by gaining the keys to 10 Downing Street.

Months before the 1979 general election, Thatcher's adviser Gordon Reece was worried that voters would find his candidate’s natural speaking voice too shrill. By chance, he encountered Sir Laurence Olivier on a train, and the master thespian recommended his voice coach from London’s National Theater. Thatcher underwent intensive training with the coach to lower her pitch and perfect a calm, authoritative tone that served her well in her political career.

After leading her party to victory in 1979, she won re-election in 1983 and 1987. When Thatcher resigned as Conservative leader and prime minister in 1990 following intra-party divisions over a controversial poll tax and the European Community, she had served 11 years and 209 days. That made her Britain’s longest continuously serving prime minister since Lord Liverpool, who led the country between 1812 and 1827.

On October 12, 1984, a time bomb planted weeks earlier by Irish Republican Army member Patrick Magee ripped through the Grand Hotel in Brighton, England, where the Conservative Party was holding its annual conference. The blast badly damaged the bathroom in Thatcher’s suite, but the prime minister was in an adjoining room and escaped unharmed. The bomb killed five people, including a member of Parliament.

Although Thatcher’s security staff wanted her to return to London immediately, she insisted on delivering her speech as planned just hours after the bombing. “The fact that we are gathered here now, shocked but composed and determined, is a sign not only that this attack has failed, but that all attempts to destroy democracy by terrorism will fail,” she told fellow party members.

In April 1982, Argentina invaded the Falkland Islands, a sparsely populated British colony in the south Atlantic claimed by both countries. In reply, Thatcher launched an amphibious attack that retook the islands 8,000 miles from London two months later. Every January 10, the Falkland Islands celebrates Margaret Thatcher Day to commemorate the anniversary of her triumphant 1983 visit to the colony.