Patriarch named in a chapter in part of OT (5)
I believe the answer is:
jacob
'patriarch' is the definition.
(patriarch in the Bible)
'a chapter in part of ot' is the wordplay.
'chapter' becomes 'c'.
'in' is an insertion indicator.
'part of ot' becomes 'Job' (book of the Old Testament).
'a'+'c'='ac'
'ac' going within 'job' is 'JACOB'.
'named in' is the link.
(Other definitions for jacob that I've seen before include "-- Rees Mogg, MP" , "Fellow" , "Father of the twelve patriarchs of Israel" , "Name of patriarch" , "Brother of Esau" .)