"It is the green-eyed monster ... " speaker (4)
I believe the answer is:
iago
'it is the green-eyed monster speaker' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for iago that I've seen before include "Ancient role" , "Evil character in Othello" , "Organ stop" , "Othello's nemesis" , "Shakespeare's jealous villain" .)