Do you know ghouls from goblins and ghosts?
agent noun suffix, also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista, from Greek -istes, from agential suffix -tes. Variant -ister (e.g. chorister, barister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish form, popularized in English 1970s by names of Latin-American revolutionary movements.