Alter-Egos of characters who take on a different role when in pursuit of their more amoral hobbies, often so they can commit crimes without fear of ruining their personal lives or acting as a "bad person" while also having a completely "normal" life when not in costume or out of character.

Often these are confused with Dissociative characters, but unlike them not all characters who have disguises or "act" in the role of a villain are Mentally Ill - indeed, many are perfectly sane and create such personas for very reasonable (if nefarious) means.

The idea of a criminal alter-ego dates back to at least the concept of the "Gentlman Thief" - in which a rich individual would take on a criminal guise during the hours of night and commit many burglaries and theft before returning to his high social status by day, in effect living two very different lifestyles : while a common trope in folklore and fiction there have been actual real life cases of the "Gentleman Thief", though it is often blurred into urban legend.

This type of villain can be considered the villainous counterpart to the Keeper of Secret Identity hero.