disbeliever

noun

1. One who disbelieves; one who does not believe.

   “How was it possible that I, a rational man, not unacquainted with the leading scientific facts of our history, and hitherto an absolute and utter disbeliever in all the hocus-pocus which in Europe goes by the name of the supernatural, could believe that I had within the last few minutes been engaged in conversation with a woman two thousand and odd years old?”