[Zope] determining Owner of an object?

A simple question, how can I determine the Owner of a ZClass instance (or any Zope object for that matter)? My users create instances of a Seminar ZClass. I did not create a SubmittedBy property (which I would fill from AUTHENTICATED_USER.getUserName()) thinking that I could easily extract this from the Owner role. I just can't see how to do it. Cheers, Darran.