John Muir was a pioneering conservationist who is widely credited with helping to preserve the Yosemite Valley in California. He was an early advocate for the preservation of wilderness areas in the United States and is often referred to as the 'Father of the National Parks'. Muir was a prolific writer and his works helped to popularize the Sierra Nevada mountain range and the Yosemite Valley. He was also a passionate environmentalist and his efforts helped to shape the modern conservation movement.