Patriarch finds actor behind some underwear (7)
I believe the answer is:
abraham
'patriarch' is the definition.
(biblical patriarch)
'actor behind some underwear' is the wordplay.
'actor' becomes 'ham' (ham actor is a kind of actor).
'behind' says to put letters next to each other.
'some' becomes 'a'.
'underwear' becomes 'bra' (bra is a type of undergarment).
'a'+'bra'='abra'
'ham' put after 'abra' is 'ABRAHAM'.
'finds' acts as a link.
(Other definitions for abraham that I've seen before include "First ancestor of the nation of Israel" , "Hebrew patriarch from whom Jews trace descent" , "first in race" , "Isaac's father" , "OT Hebrew patriarch" .)