There is a tv fantasy series that has been on for a few seasons. As is typical of network television in the US, the quality of the writing is embarrassingly bad. So it will probably stay on the air for a few more seasons. I won't name it. I don't want to make those poor staff writers feel worse than they already do, and I don't want to get sued or harassed.
The reason I mention it is that the producers cannot seem to force themselves to label anyone as being bad. The leading villain was an evil sorceress. The woman was, literally, a bloodthirsty mass murderer. She kept an entire cellar full of her victim's body parts for souvenirs. Once, when asked about the people she had killed, she snapped that she had never bothered to keep track. Yet by the end of the second season she was apparently redeemed. You see, she had adopted a kid and decided that she was "really-very-sorry". Plus she came from a dysfunctional family. So that made everything all right.
There are other characters that are equally screwed up. The thing they all have in common is that ultimately, nobody ever does anything unforgivable. Except failing to forgive, which is a paradox. One guy, for example, had a wife that ran off to see the world and left him to raise their child alone. He didn't forgive her, which made him a bad guy. The guy she ran off with, a murdering thief, is a nice guy because he's "really-very-sorry". At least for a few episodes.
The eldest prince in Kulhn is not sorry about anything. He believes his actions are fully justified. That's not to say that he is completely bad. Throughout the course of the trilogy I have tried to show him as being ruthless, selfish, and opportunistic. But he's still human. He has good points, he has people who care about him. He has things that he believes in. Ultimately, however, he is ruthless, selfish, and opportunistic.
That's the whole point of being a villain. The difference between a hero and a villain is sometimes razor thin. One of the central conflicts of my trilogy is the rivalry of two royal brothers to take their father's throne. They are full brothers. Same parents and same siblings. Raised in the same palace and taught the same ethical code. They both want the same thing, and for similar though not completely identical reasons.Both of them are willing to kill to get it. Both of them are willing to kill their own blood kin to get it.
So what's the difference? The youngest prince has an arrogant streak, and he has been guilty of behavior that is disturbingly merciless. He is also a bit judgmental toward those who disappoint him. The elder prince loves and worries about his mother, feels a deep sense of responsibility toward the men under his command and is emotionally touched by their expressions of loyalty.
The difference is where the lines get drawn. There are things that the younger prince will not do. There are lines that he will not cross. Sometimes he will push all the way up to the lines. But he will not step over them. The youngest prince acknowledges that there is a higher standard of behavior than simply his own desire, or even his own personal conscience.
The younger prince says that is is always wrong to kill the innocent, it is always wrong to rob, it is always wrong to kidnap and rape. It doesn't matter why you want to do it. The youngest prince says that there are standards which a ruler may not transgress, He is committed to the principle that a king cannot and must not rule vengefully. The law must always be applied in cold blood, no matter how heinous a crime might be. Nor can a king spare his friends because he loves them, not if they have crossed the lines. If you do something that breaks one of the absolute wrongs, then you must be called to account. Even if you are really-very-sorry.
That cannot be said of the elder prince. To the elder brother, the end justifies the means. He has never heard of situational ethics, but if he had the term would suit him perfectly. He unleashes roaming bands to scour the countryside of his own kingdom, looting his people's homes to provide supplies for his soldiers. He doesn't wish harm to the peasantry, or the weaker nobles. He just doesn't think they matter. His agents have no hesitation about torturing and killing the innocent for information with casual disregard, and the elder prince is indifferent. Again, he has nothing against the lowborn who die. He just doesn't think they matter. Any method, any tactic, is justified if it achieves the goal of getting him what he wants.
And THAT is the short definition of evil.