Carl Edward Sagan (1934-1997) was an astronomer and science popularizer.
In a March 1996 profile by Jim Dawson in the Minneapolis Star-Tribune, Sagan talked about his then-new book The Demon Haunted World and was asked about his personal 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."
Update from Tom Head, editor of Conversations with Carl Sagan (University Press of Mississippi, 2006):
Sagan resisted the atheism label and self-described as an agnostic.
In a 1981 interview with U.S. Catholic, Sagan said: "I have some discomfort with both believers and with nonbelievers when their opinions are not based on facts ... If we don't know the answer, why are we under so much pressure to make up our minds, to declare our allegiance to one hypothesis or the other?"
In a 1996 interview with NPR's Talk of the Nation, Sagan said (when asked about 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."
In a 1996 interview with NPR's Fresh Air, Sagan said: "I find that you learn absolutely nothing about someone's belief if yu ask them 'Do you believe in God?' and they say yes or no. You have to specify which of the countless kinds of God you have in mind."
In another 1996 interview, Sagan told Joel Achenbach: "An atheist has to know more than I know. An atheist is someone who knows there is no God."
In an interview with The Humanist magazine conducted after Sagan's death, his wife, Ann Druyan, said that neither she nor Sagan believed in a traditional God or an afterlife.