By Amina Mohamed, UNEP Deputy Executive Director
It was during the 1993 Vienna World Conference on Human Rights that I first met Wanagari Maathai. Our paths would cross many times in the following years.
She was a woman of great integrity, who set and achieved high standards in all aspects of her life. Women today are striving to meet these kinds of standards.
She was a trail-blazer in so many ways: becoming the first woman in East and Central Africa to obtain a PhD and, in 2004, becoming the first environmentalist to receive the Nobel Peace Prize for, in the words of the Nobel Committee, standing "at the front of the fight to promote ecologically viable social, economic and cultural development".
Throughout her work, she devoted just as much time to her role as a mother, bringing up her children well.
So numerous were her achievements, I often wondered if she had more hours in the day than the rest of us.
Wangari was the first to roll up her sleeves and get her hands dirty, whether for tree planting or at demonstrations to free political prisoners.
She was an unflinching champion of democracy and was thorough, consistent and unwavering in her beliefs and convictions.
For UNEP, she was an excellent partner who never tired of supporting the organization's ideals, such as her co-patronage of the Billion Tree Campaign. She represented UNEP with grace and conviction when requested.
Yet despite her heavy workload and long string of commitments, you would never hear her complain. Wangari took all the challenges of her work in her stride. For her, nothing was a burden.
Throughout her life, people from all backgrounds would seek her counsel on issues relating to the environment, development or democracy. She always made time for them.
She is one of a small handful of individuals whose legacy will truly be felt on local, national and international scales. In Kenya, the Greenbelt Movement she founded continues her work of championing women's rights and the environment. The 30 million trees the organization has planted to date across Africa will stand tall in her memory.
Elsewhere in Africa, she championed the continent's tropical forests, calling for better government management of natural resources, such as the Congo Basin.
The tributes that continue to be paid to her work by presidents, prime ministers and other leaders are testament to the great impact she made beyond her native Kenya.
Above all, Wangari will be remembered as a great listener, an excellent teacher, a wise counselor and a faithful friend.