Governor (5)
There are a few possibilities for this:
controller
'governor' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ruler that I've seen before include "Strip with straight edge to measure" , "Measuring stick" , "measure applied in school?" , "Graduated straight-edge" , "One who commands - often seen in the classroom" .)
'governor' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for pasha that I've seen before include "Turkish high-ranker" , "High-ranking Turk" , "foreign officer" , "Ottoman governor" , "Turkish title" .)
'governor' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for controller that I've seen before include "One holding the reins" , "Regulator" .)