A member of a sect.
A bigot.
Dogmatic or partisan.
Of, relating to, or partial to a sect.
Bigoted.
Parochial or narrow-minded.
A strict follower of a doctrine.
One who believes dogmatically in something regardless of evidence or even conclusive proof that the thing is false or was staged; one who has true-believer syndrome.
Used other than figuratively or idiomatically: see true, believer.