The influential environmental activist who authored the book "Silent Spring" is Rachel Carson. Published in 1962, this groundbreaking work highlighted the dangers of pesticides, particularly DDT, and its detrimental effects on ecosystems and human health. Carson's meticulous research and compelling writing played a crucial role in raising public awareness about environmental issues, sparking the modern environmental movement. Her advocacy contributed to significant policy changes, including the eventual establishment of the Environmental Protection Agency in the United States.