Conqueror of the Romans (4)
I believe the answer is:
hero
'conqueror' is the definition.
(I've seen this before)
'of the romans' is the wordplay.
'of' indicates the answer is hidden within the clue.
'HERO' is hidden in the letters of 'the romans'.
(Other definitions for hero that I've seen before include "lover whose lamp went out tragically" , "Principal male figure in a story" , "Man of valour" , "One looked up" , "Revered figure" .)