The Collaborative International Dictionary
Heresiarch \Her"e*si*arch\ (?; 277), n. [L. haeresiarcha, Gr. ?;
? heresy + ? leader, ? to lead: cf. F. h['e]r['e]siarque.]
A leader in heresy; the chief of a sect of heretics.
--Bp.
Stillingfleet.
Douglas Harper's Etymology Dictionary
Wiktionary
n. The founder of a heresy, or a major ecclesiastical proponent of such a heresy.
Wikipedia
The noun heresiarch (also hæresiarch, according to the Oxford English Dictionary; from Greek: , hairesiárkhēs via the late Latin haeresiarcha) is used to refer both to the originator of heretical doctrine, and to the founder of a sect that sustains such a doctrine. For example, according to Catholic doctrine, the founders of Protestantism, such as Martin Luther and John Calvin, were classed as heresiarchs as well as schismatics.
Usage examples of "heresiarch".
More people were arriving: guild-masters and journeymen, industrialists and engineers, heresiarchs in tall black hats and Scoffers in black suits with broad white collars, their swords on their belts.
For, in the first place, they ought to consider how intolerable it is, and how discordant with sound doctrine, to suppose that many, indeed, or almost all, who have forsaken the Church catholic, and have originated impious heresies and become heresiarchs, should enjoy a destiny superior to those who never were catholics, but have fallen into the snares of these others.