true believer

true believer (plural true believers)

1. A strict follower of a doctrine.
   • 1769, Firishta, translated by Alexander Dow, Tales translated from the Persian of Inatulla of Delhi, volume I, Dublin: P. and W. Wilson et al., page 4:

     When he had repoſed four years and four months in the boſom of care, rocked in the cradle of proſperity, he was brought forth, according to the cuſtom of true believers, and committed to the charge of moralifts of high fame, poliſhers of noble manners, and ſearchers of true knowledge, that they might cultivate his heaven-born genius, and teach him with dignity to rule that world which he was born to command[.]

2. 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.
3. Used other than figuratively or idiomatically: see true,‎ believer.

• true-believer syndrome