Autocratic ruler (8)
I believe the answer is:
dictator
'autocratic ruler' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for dictator that I've seen before include "Top dog like Hitler, Stalin and Franco" , "One who reads out for others to scribe" , "Authoritarian, tyrant" , "Extraordinary old magistrate" , "Eg, Stalin" .)