Her closest political relationship was not with anyone in her own party or even her own country. After her father and her husband, Reagan was the most important man in her life, so much so that the opposition accused her of "always dancing to Reagan's tune." In 1986, Thatcher controversially let the Reagan administration use British bases to make bombing runs on Libya.

Reagan reciprocated the loyalty and affection. Her autographed picture sat on the desk of his Century City office after he left the White House. And Thatcher, with typical meticulousness, pre-recorded her eulogy of Reagan after she had experienced some small strokes. At his funeral in 2004, she bowed to his coffin.

Her name also became inextricably linked with Mikhail Gorbachev's. After meeting the leader who later set the Soviet Union on a path of political and economic reform, Thatcher famously remarked that he was a man "we can do business" with.

The woman who came into office as a novice on foreign matters didn't hesitate to throw herself into them -- often controversially so, such as her stand against the use of economic sanctions as a way of breaking the back of apartheid in South Africa. Britain's vexatious relationship with the European Union was a hallmark of her tenure as prime minister, and has bedeviled her successors.

The Falklands War boosted Thatcher's popularity at home and paved the way for a landslide reelection victory. Even her controversial order to sink an Argentine cruiser, drowning 368 sailors, earned her cheering headlines from nationalistic tabloids and their millions of working-class readers.

Thatcher also held firm during the Persian Gulf War, when she admonished President George H.W. Bush not to "go wobbly" in facing down the Iraqi invasion of Kuwait.

In all, Thatcher led her Conservative Party to three election victories, in 1979, 1983 and 1987. But by the end, her imperious style as prime minister and party leader had sown serious dissent among her Cabinet members and in the parliamentary ranks, and her disastrous experiment with a new kind of local tax, quickly dubbed the "poll tax" because it charged everyone the same amount regardless of income, ignited protests across the country and a riot in the heart of London.

In November 1990, Heseltine decided to run against her on an internal Conservative Party ballot. Thatcher was in Paris when she learned that she had only barely outpolled Heseltine, not by a strong enough margin to be the uncontested leader, in the first round of voting. In spite of her pledge to "fight on -- I fight to win," she went home to discover that support from her colleagues was crumbling. On Nov. 22, 1990, Thatcher announced that she would step down from the Tory leadership and, hence, from the prime minister's job.

PHOTOS: Margaret Thatcher | 1925 - 2013

Fighting back tears, she moved out of 10 Downing St. less than a week later.

In her memoirs, she fondly recalled her years at the pinnacle of British politics and the cut-and-thrust of parliamentary debate, when "the adrenaline flows [and] they really come out fighting at me."

Her husband's death, in 2003, was a major blow. So was the onset of both mental and physical infirmity.

During Queen Elizabeth II's golden jubilee service at St. Paul's Cathedral in 2002, Thatcher's movements were tentative, though her voice rang out with conviction across the pews. Ten years later, she was too frail to attend a lunch at 10 Downing St. to celebrate the queen's diamond jubilee.

Hospital visits became more frequent, including a stay over Christmas to have a growth on her bladder removed.

Even as her health weakened, her influence endured. In 2007, a 7 1/2-foot-tall bronze statue of Thatcher -- unveiled, unusually, in her lifetime -- was placed in the House of Commons, opposite that of her fellow Tory leader Winston Churchill. Despite her obvious frailty, Thatcher was on hand for the ceremony.

"I might have preferred iron," she told a delighted crowd, "but bronze will do."