Hero FBI agent tailing false denial (7,3)
I believe the answer is:
leading man
'hero' is the definition.
(thesaurus)
'fbi agent tailing false denial' is the wordplay.
'fbi agent' becomes 'g-man' (synonyms).
'tailing' is a charade indicator (letters next to each other) (to tail can mean to go after or follow).
'false' indicates an anagram.
'denial' is an anagram of 'leadin'.
'gman' after 'leadin' is 'LEADING MAN'.
(Other definitions for leading man that I've seen before include "Protagonist" , "top fellow on stage" , "Principal actor" , "Chief actor" , "megastar?" .)