Another article suggested that the free safety could also be considered the quarterback of the defense:
Many people refer to the position as the quarterback of the defense,
because the safety needs to recognize formations, and communicate to
the rest of the defense accordingly.
The safety is usually the last line of defense, and like the middle linebacker, must be versatile. He will have coverage responsibilities, yet must also be prepared to provide run support if a running back or quarterback has gotten past the linebackers.
However, the middle linebacker, being close to the line, will often set defensive formations and call audibles to counter tendencies that he's spotted. The safety also perform that function for the defensive secondary, but might be too far away to make adjustments to the seven players in the defensive front.