The Sierra Club Founder is John Muir, a four-letter name. John Muir was an influential naturalist, author, and environmental philosopher who founded the Sierra Club in 1892. He was a passionate advocate for the preservation of wilderness in the United States and is often referred to as the 'Father of the National Parks'. Muir's activism helped to establish Yosemite National Park and Sequoia National Park, among other protected areas. His writings and activism have had a lasting impact on the environmental movement.