A leader or founder of a heresy; a person who originates or leads a religious belief that opposes orthodox doctrine.
From Greek 'hairesis' (school of thought, heresy) plus 'arkhes' (leader, ruler). The word entered English in the 16th century to describe influential heretical leaders.
Many people we now consider brilliant—like Galileo or Darwin—were called heresiarchs by religious authorities for contradicting accepted doctrine, showing how 'heresy' often just means 'being ahead of your time.'
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