a professed believer who maintains religious opinions contrary to those accepted by his or her church or rejects doctrines prescribed by that church.

Roman Catholic Church . a baptized Roman Catholic who willfully and persistently rejects any article of faith.

anyone who does not conform to an established attitude, doctrine, or principle.

heretical.

noun

apostate , sectarian , cynic , pagan , skeptic , dissenter , dissident , nonconformist , schismatic , sectary , separationist , heresiarch , iconoclast , infidel , miscreant , rebel , renegade , unbeliever