A few months ago, I discussed how Every Villain is a Hero — very few bad guys perceive themselves as bad guys, so you need to think of their motivation in heroic terms.
The story follows Malin Keshar, a young mage trying to save his village from orcs. Desperate, he uses a little necromancy in a pinch, which gets him banished from his homeland. As the twelve chapters unfold, bad decisions snowball until the story reaches a satisfyingly bleak conclusion.
Reading up on the scenario afterwards, I came upon this description of Malin’s dilemma, a trope called All of the Other Reindeer:
A character is surrounded by people who constantly put him or her down, usually because of some trait that is integral to them being a hero or villain. It seems the only responses one can make to this are the extremes: “put up with it silently” or “let them die/kill them all.”
If a hero, the character will constantly show their virtue by putting up with it and saving their tormentors’ lives again and again. Said tormentors will be grateful for about five seconds (that is, until the end of the episode), and then start it up again.
If a villain, they’ll inevitably explode and slaughter their tormentors, to the barely disguised envy of the audience. Oh, the hero will stop them eventually, but not before most of those who wronged the villain are taken out.
That’s a great roadmap for one kind of villain backstory.
And if you haven’t spent an afternoon clicking through TV Tropes, it’s well worth the time suck.