A supporter overacting as Biblical character (7)
I believe the answer is:
abraham
'biblical character' is the definition.
(Old Testament figure)
'a supporter overacting' is the wordplay.
'supporter' becomes 'bra' (a bra gives support to breasts).
'overacting' becomes 'ham' (as in a ham actor).
'a'+'bra'+'ham'='ABRAHAM'
'as' is the link.
(Other definitions for abraham that I've seen before include "Founder of the Hebrew people" , "Father of all the Jews (7)" , "Bar a ham from playing the Biblical patriarch" , "Lincoln, perhaps" , "Isaac's father" .)