Writer Paul's inside with Norse god (6)
I believe the answer is:
author
'writer' is the definition.
(I know that writer can be written as author)
'paul's inside with norse god' is the wordplay.
'inside' indicates the central letters.
'with' is a charade indicator (letters next to each other).
'norse god' becomes 'thor' (Thor is an example).
The middle of 'paul' is 'au'.
'au'+'thor'='AUTHOR'
(Other definitions for author that I've seen before include "Writer of a book, article or document" , "Originator" , "Generator, source" , "Ford, for example" , "Writer of a book, say" .)