Bad characters! Always interesting to create, some times more so than the good guys.
Most of my stories come to me first as a scene. And then another scene. And then another. Somewhere along the line there’s going to be conflict and there’s usually a bad guy or semi-bad guy appearing. I don’t often know ahead of time where they came from of what they’re story is. But I need to find out.
I hate books where the bad guy is totally bad. He’s mean, he kicks his dog, he’s a racist, he lies, he steals, and he tries to break most of the commandments. I often encounter these characters in books with important themes like race or sexual abuse. The protagonist will be multi-faceted and complex, but the bad guy is a cardboard cutout.
More often in real life, the bad guys we meet, are not bad all the time or with everyone. They may rob you, but be kind and loving to a parent. They may hate you because of your skin color, but be exceptionally loyal and trustworthy to their friends. People are complex, so should our characters be.
I think we’ve all either done or day dreamed about doing bad things. Which makes you realize, even nice people like you and I, have at least the imagination to visualize doing something wrong. I believe most people we hear about doing bad things have some sort of backstory that at least partially explains (not excuses) their behavior. The best bad characters have authors who share some of that with us (Voldemort! From Harry Potter, Judd in the Shiloh books!)
Finding out what your bad guy’s backstory is, making it interesting, and sharing some of it with your readers, could be one of the most rewarding parts of writing your story.