America's rapid progress in the early 1900s threatened to destroy wild places like Yosemite. In response, John Muir demanded a system to protect the nation's natural treasures. His tireless writing and campaigning created five national parks and an agency to care for them. Thanks to Muir, known as the "Father of the National Park Service," people can still enjoy the country's scenic and historic wonders today. John Muir and President Theodore Roosevelt left a legacy of more than 400 national parks.