Author who is not a user - Does a module exist?
The solution was clearly provided by @Clive in his comment:


  users only make sense in the context of authorisation. Since you don't
  want/need that, you should just create an 'Author' content type and
  use that to store your authors and use EntityReference to relate them
  as Nikhil suggested


If a logged in user needs to be associated with a user in order to pre-fill this author display field you could have an entity reference on the user profile page.
If this needs to be a module, use features module to export:


Author content type
Author entity reference on users
Author field base with form field and display handling


I never actually created a module for this.