Heckle King and Queen's agent (6)
I believe the answer is:
booker
'agent' is the definition.
(booker is a kind of agent)
'heckle king and queen's' is the wordplay.
'heckle' becomes 'boo'.
'king and queen' becomes 'ker' (I've seen this in other clues).
'boo'+'ker'='BOOKER'
(Other definitions for booker that I've seen before include "Literary prize" , "U.K. annual prize for best novel" .)