Your ability to be in charge, make decisions and set boundaries. This could also symbolize an authoritative figure around you. A helpful or friendly king suggests you are doing well with your ability to rule your life and decisions and those who look up to you or it can indicate a good relationship with an authoritative figure.
A dangerous or harmful king can mean you are overstepping your bounds and perhaps being too dictatorial to those around you or that someone around you is behaving this way.
The context of the dream should help you determine how well or how poorly authority or the ability to be authoritative is working in your life.