Wangari Maathai rose to prominence fighting for those most easily marginalised in Africa - poor women.
The first African woman to win the Nobel Peace Prize was praised by the awarding committee as "a source of inspiration for everyone in Africa fighting for sustainable development, democracy and peace".
Wangari Maathai has been praised for her courage and determination
A pioneering academic, her role as an environmental campaigner began after she planted some trees in her back garden.
This inspired her in 1977 to form an organisation - primarily of women - known as the Green Belt Movement aiming to curtail the devastating effects of deforestation and desertification.
Her desire was to produce sustainable wood for fuel use as well as combating soil erosion.
Her campaign to mobilise poor women to plant some 30 million trees has been copied by other countries.
Speaking as recently as Wednesday on the BBC's Africa Live programme she said her tree planting campaign was not at all popular when it first began.
"It took me a lot of days and nights to convince people that women could improve their environment without much technology or without much financial resources."
The Green Belt Movement went on to campaign on education, nutrition and other issues important to women.
Mrs Maathai has been arrested several times for campaigning against deforestation in Africa.
In the late 1980s, she became a prominent opponent of a skyscraper planned for the middle of the Kenyan capital's main park - Uhuru Park.
She was vilified by President Daniel arap Moi's government but succeeded in thwarting the plans.
More recently, she evolved into a leading campaigner on social matters.
Once was beaten unconscious by heavy handed police. On an other occasion she led a demonstration of naked women.
In 1997, she ran for president against Mr Moi but made little impact.
But in elections in 2002, she was elected as MP with 98% of the votes as part of an opposition coalition which swept to power after Mr Moi stepped down.
She was appointed as a deputy environment minister in 2003.
Mrs Maathai says she usually uses a biblical analogy of creation to stress the importance of the environment.
"God created the planet from Monday to Friday. On Saturday he created human beings.
"The truth of the matter is... if man was created on Tuesday, I usually say, he would have been dead on Wednesday, because there would not have been the essential elements that he needs to survive," she told the BBC.
The Nobel Peace Prize committee praised her for taking "a holistic approach to sustainable development that embraces democracy, human rights and women's rights in particular".
She thinks globally and acts locally, they said.
She was born in 1940 and has three children.
Her former husband, whom she divorced in the 1980s, was said to have remarked that she was "too educated, too strong, too successful, too stubborn and too hard to control".