Leading man, extremely handsome Romeo, content to leave (4)
I believe the answer is:
hero
'leading man' is the definition.
(eg the hero of a film)
'extremely handsome romeo content to leave' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'content to leave' says to hollow out the word (remove centre letters) (the contents of the word are removed).
'handsome' with its centre taken out is 'he'.
'romeo' with its centre taken out is 'ro'.
'he'+'ro'='HERO'
(Other definitions for hero that I've seen before include "Main protagonist" , "Leading male role" , "Lion" , "Admired champion" , "object of adulation" .)