Before rushing off
Please, before following the more hard-nosed advice in some of the other answers, speak privately with your other players, and see how much of a problem they feel the situation is.
When you issue an ultimatum (threatening to kick him out) the player may just leave the game to avoid the humiliation of rejection. And you have no assurance your other players will thank you if this happens. You could easily end up looking like the bad guy.
However, if you hear from your other players this fellow is ruining your fun, or worse, kind of bullying people, then act strongly to stop that behavior immediately - or just disinvite immediately.
Maintain your respectful attitude and be the grownup
At work or volunteering in the community, the rule they emphasize most is to treat people with respect and never humiliate them. Be respectful and discrete, even (especially) when you deal with issues about lack of respect. Why would it be any different when you're playing a game? It's fundamental. Nobody respects a leader who humiliates people, and people generally don't enjoy being around it.
For issues when you're meting out real discipline to a player, speak to him privately.
The only exceptions would be for behavior you would not accept outside the game, like real verbal abuse. You should correct that behavior immediately (person to person, although you are still the one in charge here) but in respectful, face-saving ways (see below).
Run of the mill boorishness
Based on your description though, it sounds like we're dealing with a mix of a lack of social skills, some over-excitement, and an unchecked desire to help the party as much as possible.
So maybe you've got regular-old bossy player who plays a bossy character. That's legitimate - most parties have a "take charge" person or two - but you will want to set limits to ensure fun for everyone.
Directing other characters in combat
The Pathfinder rules (Pathfinder Core Rulebook, p.181-182) state that characters can make free actions that "consume a very small amount of time and effort." More than that would require use of another action. Make sure everyone is familiar with the rules in that section, maybe reading it aloud. Let them know now "that everyone is familiar with the combact mechanic," you are going to be more of a stickler about extended talk during combat (in accordance with the rules) in order to speed up gameplay and make combat more exciting.
If "anyone" (wink) wants to give detailed guidance to others, that will be OK, but will require that character using its Immediate Action, or next turn's Standard Action, at your discretion. And assure them you will warn players when they've reached the limit of what you will accept as a free action, so they can stop without losing an action.
Monopolizing the Role-Playing
My favorite line from The Gamers: Dorkness Rising goes something like "If you have a problem, then solve it, in character" This is a prime example where the solution to a role-playing problem can be better role-playing. Let your NPC's do your work for you. (And be gentle, at least at first.)
An NPC might say to the bossy character:
"I really like your take-charge attitude, but I need to hear from the other members in your party."
If that doesn't help, follow with:
"Does this fellow ever stop talking?"
The NPC might say to the other characters, who are accepting directions:
"Is he...telling you what to say?"
"Do you always do what he tells you to?"
If the player objects that it's the players talking, not the characters talking, you can either say that's not possible/appropriate, or just say the NPC's are picking up on the dynamic between the characters based on the table talk.
Mix it up, though. Doing this with every NPC probably wouldn't be reasonable and could be tiresome.
You can always flip that dynamic once in a while, and see if you can provoke a reaction from the other PC's. An abrasive NPC take a liking to the bossy PC, and treats the other PC's like they were the hired help:
"I'm sure you little helper here could manage to unlock those doors for you." A little condencension can encourage folks to stick up for themselves, and point out to the "leader" just how they might be coming across.
Don't pick on people
Make sure the naturally bossy player knows you aren't picking on him, just trying to give every player their fair shakes and "screen time" in the game. Because the issue you describe is as much about drawing the other players out as reining in your Type A fellow.