Atheist,agnostic,infidel,skeptic refer to persons not inclined toward religious belief or a particular form of religious belief.  An atheist is one who denies the existence of a deity or of divine beings.  An agnostic is one who believes it impossible to know anything about God or about the creation of the universe and refrains from commitment to any religious doctrine.  Infidel means an unbeliever, especially a nonbeliever in Islam or Christianity.  A skeptic doubts and is critical of all accepted doctrines and creeds. 

atheist

The existence of a world without God seems to me less absurd than the presence of a God, existing in all his perfection, creating an imperfect man in order to make him run the risk of Hell. [ Armand Salacrou, "Certitudes et incertitudes," 1943]