John Muir, also known as "John of the Mountains" and "Father of the National Parks", was an influential Scottish-American naturalist, author, environmental philosopher, botanist, zoologist, glaciologist, and early advocate for the preservation of wilderness in the United States of America. His letters, essays, and books describing his adventures in nature, especially in the Sierra Nevada, have been read by millions. His activism helped to preserve the Yosemite Valley and Sequoia National Park, and his example has served as an inspiration for the preservation of many other wilderness areas. The Sierra Club, which he co-founded, is a prominent American conservation organization. In his later life, Muir devoted most of his time to the preservation of the Western forests.