Monster / Anime and Manga
aka: Bleach
Johan Liebert is indeed a Monster.

"I saw hell right there in his eyes. Hell. In the eyes of a living human being."
Hans Georg Schubert on Johan Liebert, Monster

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 have their own pages:

Other examples:

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