Leonard Euler.
"Euler remained a Christian all of his life and often read to his family from the Bible. One story about his religion during his stay in Russia involved the atheistic philosopher Diderot. Diderot had been invited to the court by Catherine the Great, but then annoyed her by trying to convert everyone to atheism. Catherine asked Euler for help, and he informed Diderot, who was ignorant of mathematics, that he would present in court an algebraic proof of the existence of God, if Diderot wanted to hear it. Diderot was interested, and, according to De Morgan, Euler advanced toward Diderot, and said gravely, and in a tone of perfect conviction: "Sir, ( a + bn )/n = x , hence God exists; reply! " Diderot had no reply, and the court broke into laughter. Diderot immediately returned to France."