John C. Rensenbrink (August 30, 1928 – July 30, 2022) was an American political scientist, philosopher, journalist, conservationist, and political activist. He has initiated and helped found many organizations, the most prominent of which are the Maine Green Party (1984); the Green Party of the United States (1984–87) for both of which he was a principal founder; and CREA (the Cathance River Education Alliance) 2000 to the present, a hands-on ecological education project for local schools, schoolchildren and high school students in mid-coast Maine.