Comedian's straight man (6)
I believe the answer is:
stooge
'comedian's straight man' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stooge that I've seen before include "comedy partner" , "Yes-man" , "Partner who is the butt of comedian's joke" , "A comedian's stage butt or straight man" , "Fall guy" .)