This is one example of how a person may become an ‘antagonist’ in fiction. While it is easy to create bad people who are just evil, it is more realistic to show how root causes have driven them to be who they are. All of which could have been avoided. Perhaps they can be redeemed.
This is drawn from a personal trauma, although some elements in it are speculative or conjectural.
There are two people, Person A and B. PA also has accomplices or people sympathetic, but PA is the ringleader. PB is mostly alone.
PA and accomplices had screwed over PB to the point of driving him to consider suicide. PB is figuratively broken, bruised, bloodied and wounded and is left aside. He is left to wondering “Why?”
This had poured salt into a wound created years before when PA grievously harmed PB with unjust accusations. PB had been wondering “Why?” about that ever since; this new event just made things worse, hence the consideration of suicide. PB’s discovery through one of PA’s accomplices that PA doesn’t even remember this older event just adds salt to the wound.
The “Whys?” were never addressed. PB never gets answers. PA, et al., have moved on from the event and put it behind them; after all, they were the antagonists and know the “Whys?” (if there were any) and have dealt with whatever they need to. Not so with PB. For him, hurt and pain continue and become an integral part of existence. Without understanding the “Whys?” PB never fully recovers and is changed for the worse.
PB struggles with things and tries to relate best with the reality about him but feels alone as no one really stood up and defended him during the events; and afterward others are uncomfortable or indifferent; as such he trusts others little and presumes bad motives. He tried to defend himself during the horrors, but was out gunned and outnumbered. PB also had a weak and vulnerable base from which to defend himself, being faced with certain survival issues at the same time.
His obsession with PA and the others (his frequent dwelling on the “Whys?” and such, and wishing it never happened or fantasizing about vengeance or at least something happening to bring about justice, and knowing that it will probably never come to pass has lead PB to become something of an antagonist himself; while wanting to be “good,” he feels he cannot risk that and needs to put himself and his feelings first.
Meanwhile, PA and the others are to all appearances “good people,” and if they discuss the events at all, it is to the disparagement of PB. As PB isn’t around to defend himself and no one else is willing to defend him, his reputation suffers. Only one side of the story gets told.
So, a combination of time leading PB to become “bad” and PA, et al., to become “good” has only worsened things for PB. PB was the victim; he never deserved the treatment. But due to powerlessness and no healing because PB never learned “Why?” has stunted PB and left him emotionally back where everything took place. And thus PB is ‘bad,’ not ‘evil’ but due to the woundedness and lack of answers leading to justice and healing, PB’s actions are difficult.
PB is not a “whiner,” nor one who touts “victimhood.” He has difficulty in “getting over it” but is one who is truly wounded and has never gotten the needed healing or justice.
The only thing that can heal PB is justice and knowledge. He has to know why the treatment was meted out almost to the point of driving him to suicide. PA and accomplices have to make amends, both psychological and emotional. Material amends would be a bonus, but PB knows that will never happen. (PB perhaps suffered some material loss in income over PB’s inability to manage and cope for a while.) At any rate, PA and the others have to make certain sacrifices to undo the harm they caused.
So, that’s it. A person is a victim of unjust action which were never redressed. The hurt party is still wounded despite time and some attempts at healing, but lingering issues prevent full healing. Hence, the pain has transformed him into an ‘antagonist.’
(This may be added to the backstory of a character in a novel I’m working on.)