Vigilante

A vigilante is a man or a woman who takes the law into their own hands (many vigilantes in fiction wear masks and capes - hence the popular title "masked avenger"), they can be similar to antiheroes and tend to work outside the law as some of their method includes murder or violence. However, by ignoring the justice system, a vigilante could inevitably cause troubles during their actions and had a chance to made a grave mistake by end up killing a wrongfully convicted person and worse, take an innocent life as well. For villainous version of vigilantes.