John Muir (1836-1914) - Muir spent much of his adult life wandering in -- and fighting to preserve -- the wilderness of the western United States, especially California. His tireless efforts led to the creation of Yosemite National Park, Sequoia National Park and millions of other conservation areas. Muir was a profound influence on many leaders of his day, including Theodore Roosevelt. In 1892, Muir and others founded the Sierra Club "to make the mountains glad."
Aldo Leopold (1887-1948) - The godfather of land management, wilderness conservation and of modern ecologists. After studying forestry at Yale University, he worked for the U.S. Forest Service. Though he was originally asked to kill bears, cougars and other predators on federal land because of protests from local ranchers, he later adopted a more holistic approach to wilderness management. His best-known book, A Sand County Almanac, remains one of the most eloquent pleas for the preservation of wilderness ever composed.
Rachel Carson (1907-1964) - The founder of the modern environmental movement. Born in rural Pennsylvania, she went on to study biology at Johns Hopkins University and Woods Hole Marine Biological Laboratory. After working for the U.S. Fish and Wildlife Service, Carson published The Sea Around Us and other books. Her most famous work, however, was 1962's controversial Silent Spring, in which she described the devastating effect that pesticides were having on the environment. Though pilloried by chemical companies and others, Carson's observations were proven correct, and pesticides like DDT were eventually banned.
Edward Abby (1927- 1989) - America's most dedicated -- and most outrageous -- environmentalists. Born in Pennsylvania, he is best known for his passionate defense of the deserts of America's Southwest. After working for the National Park Service in what is now Arches National Park in Utah, Abbey wrote Desert Solitaire, one of the seminal works of the environmental movement. His later book, The Monkey Wrench Gang, gained notoriety as an inspiration for the radical environmental group Earth First! which has been accused of eco-sabotage by some, including many mainstream environmentalists.
Chico Mendes (1944-1988) - best known for his efforts at saving the rainforests of Brazil from logging and ranching activities. Mendes came from a family of rubber harvesters who supplemented their income by sustainably gathering nuts and other rainforest products. Alarmed at the devastation of the Amazon rainforest, he helped to ignite international support for its preservation. His activities, however, drew the ire of powerful ranching and timber interests -- Mendes was murdered by cattle ranchers at age 44.
Wangari Manthai (1940-2011) - an environmental and political activist in Kenya. After studying biology in the United States, she returned to Kenya to begin a career that combined environmental and social concerns. Maathai founded the Green Belt Movement in Africa and helped to plant over 30 million trees, providing jobs to the unemployed while also preventing soil erosion and securing firewood. She was appointed Assistant Minister in the Ministry for Environment and Natural Resources, and in 2004 Maathai was awarded the Nobel Peace Prize while continuing to fight for the rights of women, the politically oppressed and the natural environment.
Vandana Shiva- an Indian scholar, environmental activist, food sovereignty advocate, and alter-globalization author. Shiva, currently based in Delhi, has authored more than twenty books.
Bill McKibbon- an American environmentalist, author, and journalist who has written extensively on the impact of global warming. He is the Schumann Distinguished Scholar at Middlebury College and leader of the anti-carbon campaign group 350.org.
Katharine Hayhoe-an atmospheric scientist and professor of political science at Texas Tech University, where she is director of the Climate Science Center. She is also the CEO of the consulting firm ATMOS Research and Consulting.
Al Gore- He created an Oscar winning documentary, labeled An Inconvenient Truth concerning this matter, as well as numerous books on the environmental crisis. Gore has used his political power to create organizations devoted to the problem, and speaks publicly regarding global warming. Most recently, he spoke at the 2015 Paris Climate Summit.
Jane Goodall - The British primatologist is considered the world's foremost expert on chimpanzees after her 55-year-long study on the wild chimpanzees in Gomber Stream National Park in Tanzania, but she's also a dedicated advocate and activist on behalf of animal welfare and conservation causes. Her discovery of tool manufacture and use among the chimps led her to challenge the idea that animals were distinctly different from humans, and argue instead that "we're not as different from the rest of the animal kingdom as we used to think." Today, the Jane Goodall Institute works with people around the world to develop a greater understanding of how we can help humanity while still protecting the natural world.