Margaret Hilda Thatcher, Baroness Thatcher, née Roberts (born 13 October 1925) is a British politician, the longest-serving (1979–1990) Prime Minister of the United Kingdom of the 20th century, and the only woman ever to have held the post. A Soviet journalist nicknamed her the "Iron Lady", which became associated with her uncompromising politics and leadership style. As Prime Minister, she implemented Conservative policies that have come to be known as Thatcherism.
Originally a research chemist before becoming a barrister, Thatcher was elected Member of Parliament (MP) for Finchley in 1959. Edward Heath appointed her Secretary of State for Education and Science in his 1970 government. In 1975 Thatcher defeated Heath in the Conservative Party leadership election and became Leader of the Opposition, as well as the first woman to lead a major political party in the United Kingdom. She became Prime Minister after winning the 1979 general election.
After entering 10 Downing Street, Thatcher introduced a series of political and economic initiatives to reverse what she perceived to be Britain's precipitous national decline. Her political philosophy and economic policies emphasised deregulation (particularly of the financial sector), flexible labour markets, the privatisation of state-owned companies, and reducing the power and influence of trade unions. Thatcher's popularity during her first years in office waned amid recession and high unemployment, until economic recovery and the 1982 Falklands War brought a resurgence of support, resulting in her re-election in 1983.
Thatcher was re-elected for a third term in 1987, but her Community Charge (popularly referred to as "poll tax") was widely unpopular and her views on the European Community were not shared by others in her Cabinet. She resigned as Prime Minister and party leader in November 1990, after Michael Heseltine launched a challenge to her leadership. Thatcher holds a life peerage as Baroness Thatcher, of Kesteven in the County of Lincolnshire, which entitles her to sit in the House of Lords.