I believe that Red John is Raymond Haffner but that he also Bret Stiles, huh?, some of you might be thinking but just bear with me for a moment.
Red John is connected to visualize, we know that Haffner was "on a wrong path" as a kid, he said that himself. What I believe is that he killed the two visualize members at the barn that was shown in the Red Barn episode. Bret Stiles found out and decided that it would be useful to have a "killer" like Haffner around, so he sends Haffner whenever he has a problem that he needs taken care of. Haffner however really finds that he enjoys killing and can't control his urges and own fantasies so he decides to also kill people that he wants to kill thus creating Red John. Stiles finds out and feels guilty because he realizes that he has created a monster that is the reason why Stiles occasionally helps Jane but also avoids bringing him too close to Red John.
