He was primarily an astrophysicist and astrobiologist. I feel like a total poser saying this, but I've never read any of his work. I came to know him through Coast to Coast AM's After Dark, with hosts like Art Bell and George Noory. To be clear, I think most of what that program covers is hooey, but I like that it makes you think and ponder the "impossible."
The Demon-Haunted World: Science as a Candle in the Dark is a 1995 book by astrophysicist Carl Sagan, in which Sagan aims to explain the scientific method to laypeople, and to encourage people to learn critical and skeptical thinking. He explains methods to help distinguish between ideas that are considered valid science and those that can be considered pseudoscience. Sagan states that when new ideas are offered for consideration, they should be tested by means of skeptical thinking and should stand up to rigorous questioning.
LyricalOne 