Your examples of side-characters who are potentially more important than the "main cast." The spotlights don't shine on them often, but whenever the chips are down they get things done one way or another. Maybe your hero or demon lord (etc) act only on instinct, that being their sense of "righteousness" or whatever. This character may have similar feelings, but is more "calculated" in their actions. They don't always go for the jugular, after all not everyone deserves such a quick death, nor can information necessarily be gained by such a threat ("tell me or I kill you" is not necessarily more threatening than "tell me and you will cease to suffer the hellish pain I am currently inflicting on you"). They observe, they make plans, they have contingencies for their contingencies. And if you ever actually anger them, you'll spend the rest of your short eternity wishing you hadn't.
Do you have any "side-characters" who are unimportant until they aren't? Who make things happen while staying in the background, unless the situation forces their direct (and potentially horrible) action?