Margaret Hilda Thatcher, Baroness Thatcher, LG, OM, PC, FRS (nÃ©e Roberts; born 13 October 1925) is a British politician who served as Prime Minister of the United Kingdom from 1979 to 1990. The first female British prime minister and the longest-serving of the 20th century, Thatcher's strict conservative policies, hard line against trade unions and tough rhetoric in opposition to the Soviet Union earned her the nickname the "Iron Lady". Originally a chemist, then a barrister, Thatcher became Member of Parliament (MP) for Finchley in the 1959 general election. During her time in Parliament, she heavily criticized the tax policies of the Labour Government. Edward Heath appointed Thatcher Secretary of State for Education and Science in his 1970 government. In 1975 Thatcher became Leader of the Conservative Party (and Leader of the Opposition), the first woman to head a major political party in the United Kingdom.