Lady Thatcher served from 1975 to 1990 as leader of the Conservative Party. She was called the "Iron Lady" for her personal and political toughness.
She made few public appearances in her final months, missing a reception marking her 85th birthday hosted by Prime Minister David Cameron in October 2010. She also skipped the July 2011 unveiling of a statue honoring her old friend Ronald Reagan in London.
In December 2012, she was hospitalized after a procedure to remove a growth in her bladder.
Thatcher won the nation's top job only six years after declaring in a television interview, "I don't think there will be a woman prime minister in my lifetime."
During her time at the helm of the British government, she emphasized moral absolutism, nationalism, and the rights of the individual versus those of the state -- famously declaring "There is no such thing as society" in 1987.
Nicknamed the "Iron Lady" by the Soviet press after a 1976 speech declaring that "the Russians are bent on world dominance," Thatcher later enjoyed a close working relationship with U.S. President Reagan, with whom she shared similar conservative views.
But the British cold warrior played a key role in ending the conflict by giving her stamp of approval to Soviet Communist reformer Mikhail Gorbachev shortly before he came to power.