Biblical king finally lacking as leading man (4)
I believe the answer is:
hero
'leading man' is the definition.
(eg the hero of a film)
'biblical king finally lacking' is the wordplay.
'biblical king' becomes 'herod' (I've seen this before).
'finally lacking' means to remove the last letter.
'herod' with its final letter removed is 'HERO'.
'as' is the link.
(Other definitions for hero that I've seen before include "Lamp-lighting lover" , "Exceptionally brave person" , "Man of valour" , "One shows exceptional courage" , "Chief male character in story or film - probably very brave" .)