Don John, who is a villain just because...
"...but if ever the sensible Benedick bear it, pluck off the bull's horns and set them in my forehead: and let me be vilely painted; and in such great letters as they write Here is good horse to hire, let them signify under my sign, --Here you may see Benedick, the married man."
Sometimes one needs a villain who is a villain just because!
I like Benedick's profession of love and devotion where he then offers to do Beatrice any service - only to have her demand he kill Claudio.
And of course Dogberry, who invented the malapropism long before it gained its name.