Must be a defining trait - this category is for bands that actually exist but perform in the guise of fictional characters; bands that are themselves fictional belong in Category:Fictional musical groups instead. Bands that pose as real people belong in Category:Tribute bands.
This category is for musical acts where the musicians assume the identities of fictional characters, usually characters they have created themselves. Members of such bands frequently perform in costume or masks and often come up with elaborate backstories in place of the acts actual backstory.