(n.) One who pushes a principle or measure to extremes; an extremist; a radical; an ultra.

Bolshevik Bolshevist Bolshie Carbonarist Carbonaro Castroist Castroite Charley Communist Cong Fenian Guevarist Jacobin Leninist Maoist Marxist Mau-Mau Puritan Red Red Republican Roundhead Sinn Feiner Trotskyist Trotskyite VC Vietcong Wobbly Yankee Yankee Doodle anarch anarcho-syndicalist antinomian bonnet rouge criminal syndicalist extreme left-winger extremist frondeur insurgent insurrectionist left-wing extremist lunatic fringe malcontent mild radical mutineer nihilist parlor Bolshevik parlor pink pink pinko radical rebel red revel revolter revolutionary revolutionary junta revolutioner revolutionist revolutionizer sans-culotte sans-culottist subversive syndicalist terrorist ultra ultraist yippie