I'm not certain how Zope stores the object owner. In order to correct some permissions problems (e.g. Simpleblog's "blog" objects won't display themselves when run under Zope's nobody user, which gets assigned when a user account is deleted or cannot be otherwise resolved), I had to take ownership as admin, temporarily grant myself manager privileges, and re-take ownership as xenophon. Very cumbersome. Technically, the object owner before and after this process was xenophon, yet the blog wouldn't display itself before (giving the error "Insufficient priveleges"). It must have some underlying security identifier that isn't based on the user ID.

Of course, one may only take ownership. There is no way to assign ownership to another user.