I think communication is going to be key. Most of the time based on what you are saying you are dealing with an A personality who is more focused on results rather than the office politics.

Since control is the issue you may consider defining the employees job role better so he/she understands what they should be delegating. If they can't delegate properly without being overbearing then you need to work with them to help them understand the issue. Begin by asking if they trust the other employees at the company. This question will be alarming to the employee to the extent they will know something is wrong, and that is GOOD because it provides an opportunity to open up communication issues to help solve the identified problem.

The A personalities tend to be so results driven that they don't even notice their controlling nature.

I would follow that up by coaching the employee weekly and sitting in silently on meetings with the employee and their subordinates so you can see first hand what is going on. Then hold debriefing meetings with gentle nudges in the right direction.

On the side burner, develop a company mission statement with input from employees but make sure collaboration and positive team synergy hit the list as top priorities over bottom line results.

If the employee continues to ignore the signs being sent out and is resistant to your coaching meetings, I would consider actively managing them out or even asking what their career goals are to see if they align with your companies' needs any longer.

Having a key player being a control freak can easily demotivate the rest of the team and also lead to turnover issues, so I would avoid sitting on the problem just because they are "vital" to the organization.

Don't forget, everyone is replaceable. Just a matter of how much time it takes to properly plan a transition..

I would be happy to hop on a call to discuss further and see if there are other strategies that may work based on a more detailed description of what the employee is controlling about and what kinds of ripples that is causing.