20. Jimmy Carter
Jimmy Carter was elected president in 1976 and served from 1977 until 1981 when he was succeeded by Ronald Reagan. During his time as president, he sought to move the United States away from fossil fuels. Why? Because they were causing chaos and instability in the Middle East. His efforts to create a green energy grid were unsuccessful at the time. Nevertheless, the idea of green energy has gained significant traction since his presidency. After leaving office, Jimmy Carter has been an advocate for the poor and marginalized. Plus, this former US president regularly volunteers with Habitat for Humanity by helping to build houses for those in need.