aggressor [aggressors](the person or country that first attacks or makes an aggression) noun [UK: ə.ˈɡre.sə(r)] [US: ə.ˈɡre.sər]John was clearly the aggressor. = John era chiaramente l'aggressore.
assailant [assailants](an attacker; someone who attacks another violently, or criminally) noun [UK: ə.ˈseɪ.lənt] [US: ə.ˈseɪ.lənt]