It ensures well-rounded character votes for Boris? (9)

I believe the answer is:

backstory

'it ensures well-rounded character' is the definition.
(eg a backstory for a character in a book)

'votes for boris?' is the wordplay.
'votes for' becomes 'backs' (as in backing a candidate in an election).
'boris?' becomes 'Tory' (Tory can mean a Conservative eg Boris Johnson).
'backs'+'tory'='BACKSTORY'

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app