An autocrat in the city ran things (6)
I believe the answer is:
tyrant
'an autocrat' is the definition.
(I know that autocrat can be written as tyrant)
'in the city ran things' is the wordplay.
'in' indicates a hidden word.
'TYRANT' is hidden in the letters of 'city ran things'.
(Other definitions for tyrant that I've seen before include "bully - with 17d" , "Despotic ruler" , "Totalitarian" , "Autocrat or despot" , "taskmaster" .)