Complex evil characters
For complex evil characters to work, you’ve got to give them some screen time, as it were. Because a paragraph or two simply will not cut it.
Since evil characters are a certain type of character, it pays to give them a backstory as deep and rich and meaningful as the ones you give to your hero characters. Hence, just as you do with your hero characters, think about where and when they were born. Do they have siblings? Do their parents still live? Maybe there were early signs of trouble. Could they have been abused or neglected? Did they abuse weaker, younger siblings, or animals (both of those signify deep mental disturbances)? Perhaps there is trauma.
So, why is this particular character evil? What drives their behavior? Because real human beings don’t just do bad things for fun, what gives? Are they seeking vengeance for something? Did they lose their own true love, their fortune, their family, or their home? Maybe they were horribly humiliated.
And for your complex evil characters to do their thing, they need some way of getting it done. Hence an impoverished character would need funds, probably. Or a disabled character might need someone else to be the muscle. And a famous character might simply pay someone else to do their dirty work.
Means for characters can potentially also be about weaponry. Your French medieval society would only have rudimentary use of gunpowder (Joan of Arc lived during a time of gunpowder use but didn’t necessarily use it herself). However, your evil character might just be a jerk or a person who calls others names. If that’s the case, then you should know which slurs were used when.
Your complex evil characters have limitations if they live far from your other characters. However, modern or future characters can attack in cyberspace. Or maybe they can attack over the phone or via letter if you go back in time.
Not every character gets punished, just as not every real-life criminal is caught. How do you want your story end? Or do you maybe want to open up the possibility of a sequel?
And even in prison or under a doctor’s care, not everyone changes their ways.
Your complex evil characters might want to avenge, well, nearly anything. And even if you used that as their motivation before, it doesn’t mean you can’t use it again. It can still work.
Complex evil characters can be memorable. Just ask Hannibal Lecter.