Margaret Hilda Thatcher, Baroness Thatcher , LG, OM, PC, FRS (née Roberts; born 13 October 1925) is a British politician who served as Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party from 1975 to 1990. She is the first and to date only woman to hold either post. She is also the oldest living British Prime minister.

Born in Grantham in Lincolnshire, England, she went on to read Chemistry at Somerville College, Oxford. She was selected as Conservative candidate for Finchley in 1958 and took her seat in the House of Commons the following year. Upon the election of Edward Heath in 1970, Thatcher was appointed Secretary of State for Education and Science. In 1974, she backed Sir Keith Joseph for the Conservative party leader, but after falling short he dropped out of the race. Thatcher entered herself and became leader of the Conservative party in 1975. Among other things, she defiantly opposed the Soviet Union, and her tough-talking rhetoric gained her the nickname the "Iron Lady". As the Conservative party maintained leads in most polls, Thatcher went on to become Britain's Prime Minister in the 1979 General Election.

Thatcher's tenure as Prime Minister was the longest since that of Lord Salisbury and was the longest continuous period in office since the tenure of Lord Liverpool who was Prime Minister in the early 19th century. She was the first woman to lead a major political party in the UK, and the first of only three women to have held any of the four great offices of state. She currently has a life peerage as Baroness Thatcher, of Kesteven in the County of Lincolnshire, which entitles her to sit in the House of Lords. During her tenure as Prime Minister she was said to need just four hours' sleep a night.