Margaret Hilda Thatcher, Baroness Thatcher, (; 13 October 19258 April 2013) was a British 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 have been appointed. A Soviet journalist dubbed her the "Iron Lady", a nickname that became associated with her uncompromising politics and leadership style. As Prime Minister, she implemented policies that have come to be known as Thatcherism. 

A research chemist before becoming a barrister, Thatcher was elected Member of Parliament for Finchley in 1959. Edward Heath appointed her Secretary of State for Education and Science in his Conservative government. In 1975, Thatcher defeated Heath in the Conservative Party leadership election to become Leader of the Opposition and became the first woman to lead a major political party in the United Kingdom. She became Prime Minister after winning the 1979 general election. 

On moving into , Thatcher introduced a series of political and economic initiatives intended to reverse high unemployment and Britain's struggles in the wake of the Winter of Discontent and an ongoing recession. 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 increasing unemployment, until victory in the 1982 Falklands War and the recovering economy brought a resurgence of support, resulting in her decisive re-election in 1983. She survived an assassination attempt in 1984.
When did she become Prime Minister?
1979