The Ultimate Vampire Resource and Directory

I've been researching mental illnesses lately, and I've realized how much potential the idea of people struggling with severe mental illness (like schizophrenia, multiple personalities disorder, etc.) could have on characters, heroes, and villains in fantasy stories, especially medieval fantasy. I see so much new, fresh potential in the idea that a story could focus on a character's inner war during a time when mental health is as mysterious as magic in some regards. Are there examples of this being used in some Fantasy stories? Gollum is a good example as we see his inner battle throughout Tolkien's works. I am particularly interested in stories revolving around a character's fighting his own illness and having the plot be centered around that.