Ruler of Rome -- pre revolutionary (7)
I believe the answer is:
emperor
'ruler' is the definition.
(I've seen this before)
'rome pre revolutionary' is the wordplay.
'revolutionary' indicates an anagram.
'rome'+'pre'='romepre'
'romepre' anagrammed gives 'EMPEROR'.
'of' is the link.
(Other definitions for emperor that I've seen before include "Japanese version of the king" , "Sovereign and richly-colored butterfly" , "Kaiser" , "Absolute ruler" , "Ruler; butterfly" .)