John Muir was the founder of the Sierra Club (with whom I differ on some specifics but agree on philosophy) and a conservationist/naturalist who made an enormous impact on our environment and our country. His explorations, writing, and activism spurred Teddy Roosevelt's conservation program and led or contributed to the protection of our most sacred spaces, including the Grand Canyon, Mount Rainier, Yosemite, Sequoia, and the Petrified Forest.
I liked this quote from the Sierra Club's website:
"People think, 'Oh, Teddy Roosevelt established Yosemite National Park, what a great president.' BS. It was John Muir who invited Roosevelt out and then convinced him to ditch his security and go camping. It was Muir, an activist, a single person." -- Patagonia founder and outdoor enthusiast Yvon Chouinard
A tip of the hat to a great American.