Richard Phillips Feynman (1918-1988) was a physicist with a long and distinguished career, from the Manhattan Project to quantum field theory to investigating the Challenger space-shuttle disaster. He shared the 1965 Nobel Prize in Physics for his work in Quantum Electrodynamics, the quantum-mechanical theory of the electromagnetic field.
In What Do You Care What Other People Think? (1988), Feynman described himself as "an avowed atheist" by his early youth. "I thought nature itself was so interesting that I didn't want it distorted (by miracle stories). And so I gradually came to disbelieve the whole religion." 
Denis Brian (2008). The Voice of Genius: Conversations with Nobel Scientists and Other Luminaries. Basic Books. p. 49. ISBN 9780465011391. "Interviewer: Do you call yourself an agnostic or an atheist? Feynman: An atheist. Agnostic for me would be trying to weasel out and sound a little nicer than I am about this."