Margaret Hilda Thatcher, Baroness Thatcher was a British Conservative Party politician who was the Prime Minister of the United Kingdom from 1979 to 1990 and the Leader of the Conservative Party from 1975 to 1990. She was the longest-serving British Prime Minister of the 20th Century, and is to date the only woman to have held the post. A Soviet journalist called her the “Iron Lady“, a nickname which became associated with her uncompromising politics and leadership style. As Prime Minister, she implemented policies that have come to be known as Thatcherism.