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 anti-heroes and tend to work outside the law as some of their methods includes murder or violence.

Perfect examples of a Vigilante are Dex Parios from Stumptown who tries to stop and detain criminals. Some could even be Tragic much like with Batman from the DC Comics who happens to do the exact same thing but with a tragic motif with his parents and eventually for the sake of protecting those in Gotham.

By vigilantes' ignorance to the justice system, a vigilante could inevitably cause trouble 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. That is why many vigilantes cannot count for Pure Good. Due to Vigilantes taking matters into their own hands and possibly interfering with the law which makes them anti-heroic, their chances from fitting into Pure Good would be really difficult. However it is not impossible for a vigilante to be pure good and they can end up qualifying if they have remorse, meet all the criteria and lack any corrupting qualities (e.g. Spider-Man).

For villainous version of vigilantes, see this page.