The prominent environmentalist known for founding major conservation organizations is John Muir. He played a crucial role in establishing the Sierra Club in 1892, advocating for the preservation of wilderness and national parks. Muir’s writings and activism were instrumental in promoting environmental awareness and the protection of natural landscapes in the United States. His efforts contributed to the establishment of several national parks, including Yosemite, highlighting the importance of environmental conservation. Muir’s legacy continues to inspire environmental movements and protection efforts globally.