I recommend the following:
a) Clear instructions. When he is too loud, tell him to wait for a moment please. You are the GM, you lead the group, you have the right to utter commands if it's for the greater good of the group. Don't be afraid of repercussions. He wants to play these games too. And if repercussions happen, you will survive them.
b) Clear decisions. When you GM, it's good to listen to everyone. Don't focus too much on the annoying guy, he is just a member like everyone else. At the end, decision is yours. You don't have to make perfect decisions all the time (no leader does), you 'only' have to try hard to be a good leader.
c) Explicit criticism. When you are alone with the player, tell him you didn't like a specific behavior, e.g. domineering another player, and explain why it was bad for the group. He will tell crap like 'I didn't do that'. Allow him that last word, neither agree or disagree, move on with other topics. Keep in mind it's not a discussion between equals but between GM and player. Never attack him as a person, focus on the worst behavior patterns. Don't expect miracles, enjoy small improvements. If he doesn't change at all, tell him to leave the group.
I guess these problems are not what you signed up for. It happened to me too, I have a difficult player in my group also. But I won't run away and I won't throw him out since it's a chance to grow as a person. Take it like a paladin. ;)
Some good points, here.
Also, generally speaking a DMPC or GMPC (they're just different words due to, I think, copyright) is a red flag. It's a red flag usually because it's led to the type of behavior you're describing. So, to the above advice: accept it is likely to become awkward in the campaign he's running, if you choose to stay in it. He may end up shifting the campaign to be mostly about his PC.
...Which is the other reason it comes up as a red flag at most tables.
If it does, you may wish to communicate with the other players. How do they handle it?
Finally, if your players are more interested in hack'n'slash, you might consider a game of that sort. I know that is not what you want to hear, but.
An alternative would be to drop awards for roleplay solutions in a more public manner. People tend to respond to rewards, and I've found many gamers to be very goal-oriented.