Monster / Anime and Manga
aka: Bleach

Johan Liebert is indeed a Monster.

Dr. Tenma: You can't just go around killing!
Johan: Why not?

Anime and manga creators have created a wide variety of villains, and some of them, like the ones on this page, are utterly horrific in their cruelty and depravity.

The following series/franchises have their own pages:

Other examples:

Alternative Title(s): Naruto, Berserk, Anime And Manga A To H, Anime And Manga I To R, Anime And Manga S To Z, Bleach