After witnessing the devastation of a 1971 San Francisco oil spill, Francis gave up motorized transportation and chose to stay silent. But it wasn’t the silence of apathy. It was a roaring silence that’s still being heard. His marathon wordless walk (recounted in his book Planetwalker: 22 Years of Walking. 17 Years of Silence) helped him reconnect with nature and inspired his earth-stewardship group Planetwalk.