Margaret Hilda Thatcher, Baroness Thatcher, (née Roberts; 13 October 1925 – 8 April 2013) was a British stateswoman and Conservative politician who was Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party from 1975 to 1990. She was the longest-serving British prime minister of the 20th century and the first woman to hold the position. As prime minister, she implemented economic policies known as Thatcherism. A Soviet journalist dubbed her the "Iron Lady", a nickname that became associated with her uncompromising politics and leadership style.

Thatcher studied chemistry at Somerville College, Oxford, and worked briefly as a research chemist before becoming a barrister. She was elected Member of Parliament for Finchley in 1959. Edward Heath appointed her secretary of state for education and science in his 1970–1974 government. In 1975, she defeated Heath in the Conservative Party leadership election to become leader of the opposition, the first woman to lead a major political party in the UK.

On becoming prime minister after winning the 1979 general election, Thatcher introduced a series of economic policies intended to reverse high inflation and Britain's struggles in the wake of the Winter of Discontent and an oncoming recession. Her political philosophy and economic policies emphasised greater individual liberty, the privatisation of state-owned companies, and reducing the power and influence of trade unions. Her popularity in her first years in office waned amid recession and rising unemployment.