> Otherwise though, I found that his personas largely reflected his current emotional state. One persona would almost always be "out" when he was upset with a friend, or struggling with some stress. Another was more childlike and playful. He described them as always there, and even though he appeared to allow one of them to be "in charge" as he put it, he said the voices were always in the back of his mind, directing his thoughts.

That doesn't sound like a disorder. The abnormal thing about your friend is that he is more aware than the average person.

The illusion of a single, unified self is just that. When you talk to people in your dreams, who are you talking to? Their responses are quite intelligent, if you listen. When you say embarrassing things under anesthesia with no memory of it, who said those things? When you get irrationally angry, who the hell is it that comes out? Same with the alcoholic who swears one day he'll quit and forgets about it the next day -- different people.

Moreover, there are huge areas of your brain that work quietly and subconsciously (from your perspective). Not only are they conscious, they're smarter than you. They prove it through intuition and gut feeling, if you listen.

> while his condition lent itself to occasional mood swings, he made a point of _respecting_ his voices, allowed them to become a part of him, and I feel had largely learned to cope.

I'm sure you didn't mean it this way, but I found your tone somewhat condescending. It's not his alternate selves that he needs to "cope" with, but society's notion that something is wrong with him. This might sound too new-age for people, but the more aware you are, the more you realize just how sick everyone else is. We literally have conscious beings imprisoned within us.

> He had figured himself out for better or worse

Probably figured himself out better than the rest of us ever will.