factionist
/ˈfakʃ(ə)nɪst/ /ˈfakʃənɪst/noun
A creator or leader of a faction; a member or supporter of a faction.
adjective
Of or relating to factionists; = factionalist.
Origin
Early 17th century; earliest use found in William Barlow. From faction + -ist. With the use as noun compare earlier factionary, factioner.