Othello antagonist (4)
I believe the answer is:
iago
'othello antagonist' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iago that I've seen before include "Othello's ensign" , "Othello's enemy" , "Evil character in Othello" , "Othello's Ancient" , "Othello's nemesis" .)