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The doctrinaire preacher was laughed upon for his crazy ideas.
Rigid, inflexible, doctrinaire.
strict, severe, autocratic, dictatorial, dogmatic, tyrannical, doctrinaire
Horace Samuel Merrill has written:
'William Freeman Vilas, doctrinaire democrat'
Some synonyms are bluestocking, bookworm, doctrinaire, dogmatist, egghead, methodologist, or pedagogue. (Or if you're really feeling informal, a dork.)