I've found two idioms with the sense "to be in charge, to give the orders":
To run the show,
To call the tune/ shots (from the expression: He who pays the piper calls the tune (19th c.)
Are these phrases common in your country? Or do you use other idioms with the same sense?
The headteacher is Dr Jobsworth, but it's his deputy who runs the show.
The new headteacher runs the show rather more efficiently than his predecessor.