User blog comment:Inferno Pendragon/The Purge Begins/@comment-24859393-20160201003604/@comment-366087-20160201005339

I always accepted that Alucard was under a geas to the Hellsings with Lady Integra the most recent one to inherit the leash.

If this is not already a Category, may I recommend Geas for Villains held in check by anyone, Villain or Hero.