Carl Sagan (November 9, 1934 – December 20, 1996) was an American astronomer, astrophysicist, author, cosmologist, and highly successful popularizer of astronomy, astrophysics and other natural sciences. During his lifetime, he published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. In his works, he advocated skeptical inquiry and the scientific method.
When asked about his religious beliefs:
“Where’s the evidence? Now, the word God is used to cover a wide variety of very different ideas, ranging maybe from the idea of an outsized light-skinned male with a long white beard who sits in a throne in the sky and tallies the fall of every sparrow–for which there is no evidence, none at all–to the view of Einstein, of Spinoza, which is essentially that God is the sum total of the laws of nature. And since there are laws of nature … if that’s what you mean by God, then of course there’s a God. So everything depends on the definition of God."
When asked about his spiritual views:
"My view is that if there is no evidence for it, then forget about it," he said. "An agnostic is somebody who doesn’t believe in something until there is evidence for it, so I’m agnostic."
Carl Sagan described himself as agnostic.
In episode 10 of his famous TV series Cosmos: A Personal Voyage, he discusses the ‘God’ question: