Burt Lancaster was an American Academy Award-winning actor who came to be regarded as one of the best actors of his generation. His films include Elmer Gantry, From Here to Eternity, Birdman of Alcatraz, The Crimson Pirate, Marty, and Sweet Smell of Success. 
Lancaster's biography on the International Movie Database notes that he was a "self-described atheist", but also mentions that some of his friends disputed this. The article also notes that he took on the role of corrupt evangelist in the film Elmer Gantry (1960) because he wanted to make an anti-Billy Graham statement.
In Kate Buford's biography about him, Burt Lancaster: An American Life (pp. 189), she writes about him returning down the eponymous role in the film Ben Hur:
"Though ostensibly an atheist since circus days, he found the movie "a belittling picture of Christianity as I understand it."
Lancaster split up with longtime girlfriend, Jackie Bone, due to her rediscovering her Christian faith, which he felt he could not share with her. 
Another passage from Kate Buford's Burt Lancaster: An American Life (pp. 277):
Bone [Lancaster's long-time girlfriend] remains certain that he was never the atheist he claimed to be, that "something happened, somewhere--perhaps hs mother's death--to turn him off" from what he still, deep down in his Elmer Gantry heart, believed. He tossed off any such identification. The Ten Commandments, he said, were fine--but not for him. 
A second biographer, Gary Fishgall, is supposed to have noted Lancaster as an atheist in his book [Against Type: The Biography of Burt Lancaster]. However, I do not have an exact quote.