It's simple, really. Magic Dreamland Entertainment did (and still does) quite a bit of business under their acronym, M.D.E. It was only a matter of time before some Knowlsian press-schmup thought he could be clever by turning "M.D." into "Doctor." Hence "M.D.E." becomes "Doctor E."
Fez Bejo, CEO of Magic Dreamland Entertainment, and the youngest entertainment industry senior exec in three centuries, toyed briefly with the idea of changing his last name to "E," and granting himself an honorary doctorate (in "fun") from The Correspondence University of Tokyo3. Fortunately his publicist talked him out of it.
Addendum to Note:While it is still possible to get a doctorate in fun from CUT3, it has no relation whatsoever to the original Doctor Fun.