In Star Wars (Episode IV), Darth Vader was what you might call a cardboard cutout of a villain. We never had any inkling of his motivations, hopes, desires, or fears; we knew nothing of his inner life at all. Yet Vader was a great villain. This goes against a doctrine in fiction which became popular in my youth that “two dimensional” villains were bad. Villains must have backstory and motivation!
Where did the doctrine of the three dimensional villain go wrong? It went wrong by not understanding perspective. A cardboard cutout is uninteresting because you can clearly see that the two dimensions are all there is to it. A shadow, by contrast, is interesting, because you know that there is something far more complicated to the shadow which you’re just not seeing. Further, villains are very difficult to make interesting for the very simple reason that in reality evil is banal. “The banality of evil” is, I believe, a phrase coined by the philosopher Hannah Arendt when she observed (and possibly interviewed) the leaders of the Nazis after the fall of the Third Reich. They had done monstrous amounts of evil, but were utterly unimpressive as people. Not only unimpressive in their persons, they were unimpressive even in their hatred. The men who had (through orders given to others) murdered millions of Jews didn’t even hate the Jews particular more than other people. It seemed like there should be something equally grandiose to the magnitude of the evil done, but there were just some small, unimpressive, even pathetic, men. This of course follows necessarily from the fact that evil is a privation of good. A man can be very, extremely good, but the maximum amount of nothing he can be is, well, nothing.
All of this adds up to the fact that realistic villains are very hard to make interesting. That is perhaps why so many people, in their desperation to do so, turned their villains into misunderstood heroes. It is not impossible to make genuinely interesting villains who are fleshed out—of these, Shakespeare’s Iago is the greatest—but the fact that it is hard means that those who are not up to the task should not try. In cases where you can’t show something, it is best to only hint at it. Readers have imaginations of their own, and if you give them an outline they will flesh it out, with more imaginative readers fleshing it out better than you would have. And even where they don’t, people can be content to not know everything, trusting that what they don’t know is rationally consistent. And as long as you don’t give inconsistent details in your shadow, that’s possible. It’s also where so many villains in the 1990s (and beyond) went wrong—they were fleshed out in ways that were completely incompatible with their actions.
The most egregious example which comes to mind is the Reavers in Firefly/Serenity. When they were mysterious, it was possible for them to be part of some ultra-satanic cult of madmen. Once they were turned into scientific zombies, they became ridiculous. Once fleshed out as victims of a peace-drug experiment, it made precisely no sense how they could cooperate well enough to pilot space ships, even space ships they didn’t take the best care of. The problem with high technology is that it requires complex maintenance. The Firefly would, fairly often, have gone nowhere had it not been for Kylie’s work in engineering. Somehow we’re to believe that rage-monsters managed to keep spaceships going with less work? Why? Did the rage-monsters luck into brand-new spaceships which could go ten thousand light years before their first scheduled maintenance? How did the drug-addled rage monsters even manage to navigate from one place to another? Because they were flesh out badly, there is no rational consistency possible for the viewer to imagine exists.
In short, the golden rule of story telling is: only flesh out what you can flesh out well.