noun

a person who rejects accepted opinions, especially those concerning religious belief.

nonconformist,individualist,independent,maverick,dissenter,heretic,libertine,agnostic,atheist,non-theist,non-believer,unbeliever,disbeliever,sceptic,doubter,doubting Thomas,apostate,humanist,pagan,heathen,infidel,paynim,renegade,nullifidian