Leading man died during Advent (10)
I believe the answer is:
commanding
'leading' is the definition.
(thesaurus)
'man died during advent' is the wordplay.
'died' becomes 'd' (abbreviation next to the year of someone's death).
'during' is an insertion indicator.
'advent' becomes 'coming' (synonyms).
'man'+'d'='mand'
'mand' placed into 'coming' is 'COMMANDING'.
(Other definitions for commanding that I've seen before include "Impressive" , "Powerful" .)