My character isn't ever mentally stable at any point in the story, but over time and because of the influence of other's manipulation, he becomes much, much worse. At the end of the story, he believes himself to be God. My dilemma is that I don't know how exactly to write a character who slips into madness. He starts out feeling out of place, distant from others, like an outsider, and has some violent tendencies, very little compassion, and is a control freak. Very shy as well. The throughout the story he is manipulated by others who notice these qualities and use him like a puppet so they can achieve an end to their means. I just am unsure of how to write it so that he is noticeably getting worse and worse and so it doesn't just seem like one day he went completely batshit crazy and was like "LOL I'M GOD NOW". Any advice on how to write someone with a gradual descent into madness or anything I could read, such as a novel about a character who has done so, would be appreciated.