Worker on Iago, heartless character in Shakespeare (7)
I believe the answer is:
antonio
'character in shakespeare' is the definition.
(character in The Merchant of Venice)
'worker on iago heartless' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'heartless' means to remove the middle letters.
'iago' with its middle taken out is 'io'.
'ant'+'on'+'io'='ANTONIO'
(Other definitions for antonio that I've seen before include "merchant threatened by weight loss" , "Shakespearean merchant" , "sea captain in Twelfth Night" , "One contracted for a pound" , "Pound of flesh promiser" .)