(n.) A supporter of extreme doctrines or practices; one who holds extreme opinions\.

Bolshevik Fabian Jacobin Wobbly agitator anarchist anarchistic anarcho-syndicalist bigoted brawler extravagant extreme extreme left-winger extremistic fanatic frondeur haggard inordinate insubordinate insurgent insurrectionary insurrectionist insurrecto irrational left-wing extremist lunatic fringe malcontent maverick meliorist mild radical mildly radical mutineer nihilist nihilistic nonconformist overenthusiastic overreligious overzealous parlor Bolshevik parlor pink perfervid pink pinko progressionist progressist progressive progressivist rabid radical rebel red reformer reformist revisionist revolter revolutional revolutionary revolutionist rioter sans-culotte subversive syndicalist traitor ultra ultraconservative ultraist ultraistic ultrazealous unreasonable utopian utopist wild-eyed wild-looking yippie zealotic