Synonyms for Fanatic (same or very similar meaning)
WordNet sense 1 (a person motivated by irrational enthusiasm (as for a cause)):
fiendWordNet sense 2 (marked by excessive enthusiasm for and intense devotion to a cause or idea):
fanatical, overzealous, rabidWordNet sense 3 (having or expressing strong emotions):
passionateFrom the ODE community, based on WordNetadd/edit