I recently had a fellow writer comment that Roi, the antagonist for Warrior Tithe, gave them “Ramsay Bolton vibes”. I took it as a compliment. A character readers love to hate.
However, I want to say this. Cu Roi mac Daire is a legendary figure from The Ulster Cycle, not someone suffering from mental illness. Bláthnat, his wife in the legend (and in my story) meant nothing but a war prize to Roi. He claimed her when he and Cu Chulainn raided her father’s castle. She gave Cu Roi’s secret to Cú Chulainn to escape a husband she never wanted, not because he was canonically, in the legend or in my story, cruel and abusive to her. I think that makes for a better story than a boy that was cruel because his daddy was cruel to him.
In my story, Roi is not a narcissist or a sociopath. He struggles with some of the choices he makes and has his regrets. He has several chances to do the right thing, but rationalizes that saving his skin, staying immortal, and staying king is worth the lives he ruins and takes.
Usually, victims of abuse do not turn into violent criminals. People who suffer from mental illness are not inherently violent, and it is time that writers stop using mental illness as a villain trope.