In my opinion, you need to drop this guy. It sounds like his code is unreadable and he is definitely not a team, nor a safe, player.
It is also a very bad practice to allow someone to see themselves as indispensible. If you let him keep this up, his practices will get worse, not better. When he leaves, for everyone does, you will be left with an enormous headache of tangled code. You need to cut your losses now if he will not shape up.
Finally, keeping this developer without reigning him in sets a poor example from junior developers. If you force them to work correctly, you risk resentment from the "why him and not me" crowd. If you don't, you get a bunch of hacks who work like your "star."
In short, unless he shapes up very, very quickly, it's time to drop him, for the health and sanity of your entire development staff.
