In her own country she's an uncrowned queen; a slight, fragile but unbending figure glimpsed by few but known to all as The Lady. Beyond it, she has become an icon, a universal symbol of courage, endurance and peaceful resistance, a new Mandela.

The word's a commonplace but Aung San Suu Kyi really is a legend: daughter of the man who won Burma its independence from the British, but who was assassinated when she was barely two; a political leader herself who for the past 22 years has headed, with a delicate but compelling charisma and unimaginable determination, her nation's "second struggle for independence"; a prisoner of one kind or another for 15 of the past 20 years; and winner, in 1991, of the Nobel peace prize.

Those who have met her (which isn't many, recently) speak of a beauty every bit as striking as the photographs, a proud poise and a demure gentility acquired, certainly, at the Anglo-Indian finishing school she attended in New Delhi, where her mother was ambassador.

She apparently also has, though, a quick and by no means prim wit and an infectious giggle. Not, by all accounts – including her own – a born political strategist, she knows precisely the system her country needs, if not precisely how to get there. Her Nobel citation called her a shining example of "the power of the powerless".

Born on 19 June, 1945, two years before independence, Aung San Suu Kyi – the name means "a bright collection of strange victories" – left Burma with her mother in 1960. In 1964 she was at St Hugh's, Oxford, studying politics, philosophy and economics. A friend, Ann Pasternak Slater, recalls her "tight, trim lungi [Burmese sarong] and her upright carriage, her firm moral convictions and inherited social grace".

She worked as a research assistant at the University of London and then for the UN in New York. She got engaged to Michael Aris in 1971, and wrote to him every day before their marriage the following year: "I only ask one thing," she said: "That should my people need me, you would help me to do my duty by them." She added: "I am beset by fears that circumstances and national considerations might tear us apart."

It took 16 years for that need to arise. Michael and Aung San Suu Kyi's first son, Alexander, was born in London in 1973, followed by their second, Kim, in Oxford, where Michael had a junior fellowship. She resumed her own academic career, teaching Burmese studies and taking research assignments first in Japan, and then in India. One evening in Oxford in late March 1988, the boys in bed, Aung San Suu Kyi took the phone call that changed her life: her mother had suffered a severe stroke.

Back in Burma, the military dictatorship that had run the country since 1962 was suppressing a student-led protest movement. On 8 August 1988, soldiers fired into a peaceful demonstration, killing up to 5,000 protesters. Barely two weeks later, Aung Sun Suu Kyi addressed 500,000 people at the great Schwedagon pagoda in Rangoon. As her father's daughter, she said, she could not stand by. "True," she said, "I have lived abroad. It is also true that I am married to a foreigner. These facts have never lessened my love and my devotion for my country." She demanded freedom and democracy, a multi-party government, and free and fair elections.

The rest is as sad as it is familiar. The National League for Democracy was formed with Aung San Suu Kyi as its general secretary.

"We listened to the voice of the people, that our policies might be in harmony with their legitimate needs and aspirations," Aung San Suu Kyi wrote. "We explained why, in spite of its inevitable flaws, we considered democracy to be better than other political systems. Most important, we sought to make them understand why we believed political change was best achieved through non-violent means."

Despite detentions and intimidation, the NLD won 82% of the seats in Burma's parliament in the 1990 elections, whose results the dictatorship have never recognised. Aung San Suu Kyi was held under house arrest until 1995, and then banned from travelling. In 1999 her husband died of cancer in London; had she left the country to visit him, she would never have been allowed back in. Detained again in 2000, released again in 2002, she was rearrested once more in May 2003. Her phone line cut, her post blocked and her NLD colleagues banned from visiting her, she has lived under house arrest at her home on University Avenue, Rangoon, ever since, writing, reading, exercising and meditating. Not even the UN secretary general, Ban Ki-moon, was allowed to meet her on a visit in 2009.

Then John Yettaw, a confused American, swam across the lake by her house to see her, ensuring she was charged and convicted with breaking the terms of her house arrest and sentenced to 18 months further house arrest – until tomorrow, a convenient six days after Burma's recent elections. "It is not power that corrupts, but fear," Aung San Suu Kyi once wrote. "Fear of losing power corrupts those who wield it, and fear of the scourge of power corrupts those who are subject to it." But even under the "most crushing state machinery, courage rises up again and again. For fear is not the natural state of man."