YANGON, June 21, 2012 (AFP) - Aung San Suu Kyi's two-decade struggle has won her a place among the world's best-known voices against tyranny, but the Nobel laureate did not always appear destined for a life of political activism.

The daughter of Myanmar's independence hero General Aung San left her homeland as a child and studied at Oxford University before marrying a British academic, appearing to settle into life in her nation's former colonial ruler.

The mother-of-two -- who turns 67 on Tuesday -- was thrust into the role of national heroine almost by accident after returning to the country formerly known as Burma in 1988 to nurse her sick mother.

Soon afterwards protests erupted against the military rulers, who crushed the uprising with a crackdown that left at least 3,000 people dead.

Suu Kyi proved to be a charismatic orator and took a leading role in the burgeoning pro-democracy movement, delivering speeches to crowds of hundreds of thousands and helping to form the National League for Democracy (NLD).

Alarmed by the support she commanded in Myanmar, where she is known simply as "The Lady," the generals ordered her first stint of house arrest in 1989. She was locked up by the junta for a total of 15 years.

Despite her confinement, the NLD swept elections in 1990 by a landslide, but was never allowed to take power.

A year later Suu Kyi won the Nobel Peace Prize, accepted by her sons on her behalf, elevating her to a profile similar to that enjoyed by Nelson Mandela as one of the world's leading defenders of human rights.

"People of Mynamar, or Burma, take enormous pride in Aung San Suu Kyi getting the Nobel prize," said Thailand-based activist-in-exile Aung Naing Oo.

"A lot of people consider it as a recognition of their long struggle against military rule."

Suu Kyi's soft-spoken approach belies a steely determination that saw her spend six days in her car in 1998 on a bridge near Yangon after the junta blocked her path.

Determined to travel outside the city, she only returned home when a soldier grabbed the wheel and drove her back.

Her struggle for her country has come at a high personal cost: Suu Kyi was unable to see her husband Michael Aris before his death from cancer in 1999, and missed seeing her sons grow up.

The then-ruling junta refused Aris a visa to visit her and Suu Kyi did not attempt to leave Myanmar during her few periods of freedom because of concerns that she would never be allowed to return.

After a third spell locked up, she was released from seven straight years of house arrest in 2010 just days after controversial elections that were dismissed as a sham by the West and won by the military's political proxies.

Since then, however, President Thein Sein has overseen a series of dramatic political reforms, releasing hundreds of political prisoners and welcoming the NLD back into mainstream politics.

Suu Kyi herself has undergone a remarkable transformation from imprisoned icon of the democratic struggle to a key player in the country's political process.

She won her first ever seat in politics in by-elections held in April, and has built a relationship of trust with Thein Sein, a former general, giving her the confidence to leave the country for the first time in 24 years to travel first to Thailand and now for a historic tour of Europe.

Her trip "signifies Myanmar is a new country and she has trust in the system," said Aung Naing Oo. "It clearly demonstrates that Myanmar is no longer a pariah state. Myanmar is part of the international community now."

Suu Kyi's health has been a concern as she has fallen ill several times in recent months because of exhaustion.

She cancelled a dinner with Swiss President Eveline Widmer-Schlumpf on Thursday after cutting short a press conference where she had vomited.

After years of favouring harsh measures against the regime, Suu Kyi has said she is optimistic about her country's future and wants to achieve change through peaceful negotiation rather than an Arab Spring-style uprising.

"What has to be done is a revolution of the spirit," she told AFP in an interview last September. "A real revolution takes a long time to be completed."