Villainous character, one in the past (4)
I believe the answer is:
iago
'villainous character' is the definition.
(villain in Shakespeare's Othello)
'one in the past' is the wordplay.
'one' becomes 'i' (roman numeral).
'in the past' becomes 'ago' (synonyms).
'i'+'ago'='IAGO'
(Other definitions for iago that I've seen before include "Shakespearean villain" , "The villain who tricked Othello" , "Organ stop" , "Othello's nemesis" , "villainous ensign" .)