The famous environmentalist known for his work in conservation is John Muir. Muir was a naturalist and advocate for the preservation of wilderness in the United States, instrumental in establishing national parks such as Yosemite. His writings eloquently conveyed the beauty and importance of nature, advocating for environmental protection and awareness. Muir co-founded the Sierra Club, which continues to be a significant force in conservation efforts today. His legacy reflects the enduring connection between human well-being and the natural world.