Denis Allen Hayes (born August 29, 1944) is an environmental advocate and proponent of solar power. He rose to prominence in 1970 as the coordinator for the first Earth Day.
Hayes founded the Earth Day Network and expanded it to more than 180 nations. During the Carter Administration, Hayes became head of the Solar Energy Research Institute (now known as the National Renewable Energy Laboratory), but left this position when the Reagan Administration cut funding for the program. Since 1992, Hayes has been president of the Bullitt Foundation in Washington and continues to be a leader in environmental and energy policy. In 2015, he is completing a fellowship at the Robert Bosch Academy to write a book on solar energy.
Hayes has received the national Jefferson Awards Medal for Outstanding Public Service as well as many other awards. Time Magazine named him as “Hero of the Planet” in 1999.