The first female Prime minister of Great Britain, Margaret Thatcher was known as Great Britain's "Iron Lady" for her refusal to be intimidated, her emphasis on individual responsibility and her deep belief in the free market system. She developed a close relationship with U.S. President Ronald Reagan and is credited with him in bringing the Cold War to a close with the collapse of the Soviet Union. She was also intensely skeptical of allowing Britain to merge with the European Union. She campaigned successfully to preserve the British pound when other European nations adopted the Euro as their currency. Today she is credited with keeping Great Britain aloof of much of the EU's fiscal problems while enjoying the benefits of the continent's open borders and markets.