Star of 'Argo' isn't top unfortunately (11)
I believe the answer is:
protagonist
'star' is the definition.
(thesaurus)
'argo isn't top unfortunately' is the wordplay.
'unfortunately' is an anagram indicator.
'argo'+'isnt'+'top'='argoisnttop'
'argoisnttop' with letters rearranged gives 'PROTAGONIST'.
'of' acts as a link.
(Other definitions for protagonist that I've seen before include "Leading character in a play, novel, etc" , "Hero" , "Lead character" , "Key character in a novel" , "Advocate" .)