There is a list for characters who have commited mass murder or genocide, defined as killing four or more people in a single incident. These ones are villains or tipically anti-heroes, varying on your belief they still killed. This list also include comic book dictators and blue-collar supervillains, who are more inclined to commit anyone in their path. Teams of supervillains inclueded as well.
EDIT: I made some clean up on this list because at the time I created it was a early user and not aware of the site's rules. So some items and profanity will be removed to accommodate the list better.