The first female Prime Minister of the United Kingdom was Margaret Thatcher. She served as Prime Minister from 1979 to 1990, becoming the leader of the Conservative Party and known for her strong, assertive leadership style. Thatcher's policies, often referred to as "Thatcherism," emphasized free-market principles, deregulation, and a reduction in the power of trade unions. She was a controversial figure, credited with revitalizing the British economy in some respects but also criticized for widening income inequality. As a pioneering female leader, she remains a significant figure in British political history and global politics.