John Muir was the co-founder of the Sierra Club, an environmental organization dedicated to protecting and preserving the environment. Muir was a Scottish-American naturalist, author, and early advocate of preservation of wilderness in the United States. He was also a key figure in the creation of the National Park System. Muir's activism helped to preserve the Yosemite Valley, Sequoia National Park, and other wilderness areas. He is remembered as one of the most influential conservationists of the 20th century.