grand vizier

noun2

1. •
   A figure of great authority and power.

   • But the ultimate fix came from the grand vizier of New Orleans voodoo-funk, Dr John, whose mesmerising performance was as close as you'll come to witnessing a shaman summoning spirits. — 2012
2. •
   (historical) The greatest minister of a sultan, with absolute power of attorney and, in principle, dismissable only by the sultan himself.