Margaret Hilda Thatcher, Baroness Thatcher, (; 13 October 19258 April 2013) was a British politician and who served as 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 that office. 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 became known as Thatcherism.