leader of a heretical movement
• (n.) A leader in heresy; the chief of a sect of heretics.
Her'e·si·arch noun [ Latin haeresiarcha , Greek ...; ... heresy + ... leader, ... to lead: confer French hérésiarque .] A leader in heresy; the chief of a sect of heretics. Bp. Stillingfleet. 
heresiarch A founder or leader of heresy.