Representative in European city upset ruler (7)
I believe the answer is:
emperor
'ruler' is the definition.
(I've seen this before)
'representative in european city upset' is the wordplay.
'representative' becomes 'rep' (rep is a kind of representative).
'in' is an insertion indicator.
'european city' becomes 'rome'.
'upset' says the letters should be written backwards.
'rep' put inside 'rome' is 'rorepme'.
'rorepme' reversed gives 'EMPEROR'.
(Other definitions for emperor that I've seen before include "Absolute ruler" , "chap such as Charlemagne" , "Sovereign - ruler" , "Ancient Roman ruler" , "noted by Beethoven" .)