Via some detours of reasoning and searching, I managed to find out who
currently owns the rights in the Mutt & Jeff cartoons. Let me give you
the background story first:
The creator of Mutt & Jeff, cartoonist Harry Conway "Bud" Fisher (b.
1884 or 85; d. 1954), who had become very wealthy thanks to the
success of his comic strip, had married Countess Aedita DeBeaumont (b.
1889; d. 1985). Later they divorced, but Aedita DeBeaumont
nevertheless inherited the rights in the Mutt & Jeff comics after Bud
Fisher had died in 1954.
The United States Copyright Office database reflects this; in numerous
entries, ownership in the Mutt & Jeff cartoons is claimed by Edita S.
DaBeaumont [the typos derive from the database entries].
This recent (2005) online publication of Mutt & Jeff cartoons, on the
uComics.com website, bears the ownership notes "by Pierre S. De
Beaumont" and "© 1993 Pierre S. De Beaumont".
It is only logical to assume that Pierre S. DeBeaumont, who very
obviously currently owns the rights in the cartoons, is a relative of
Aedita DeBeaumont and inherited the rights from her.
The United States Patent and Trademark Office lists a registered
trademark "Mutt & Jeff", relating to a 'cartoon strip, regularly
published in newspapers'. The trademark was renewed regularly (most
recently on 15 July 2000), and the owner is Pierre S. DeBeaumont.
This shows that the comic strip is indeed owned by Mr. DeBeaumont,
since otherwise he certainly would not bother to continue paying the
trademark registration fees.
As contact information for Pierre S. DeBeaumont, the Patent and
Trademark Office lists the following:
DeBeaumont, Pierre S.
P.O. Box 1528
Manchester, MA 01944
I also found Mr. DeBeaumont listed in the telephone directory, but I
am bound to the Google Answers regulations, so I am unfortunately not
allowed to publish his address here.
I hope that this will be useful!
United States Patent and Trademark Office: Trademark Database
United States Copyright Office: Copyright Database
uComics.com: Mutt & Jeff en Español by Pierre S. De Beaumont
Switchboard Telephone Directory
RootsWeb: Social Security Death Index
Michigan State University Libraries: Reading Room Index to the Comic Art Collection
Don Markstein's Toonopedia: Bud Fisher
Don Markstein's Toonopedia: Mutt and Jeff
Rich Morrissey (RMorris306): "Re: Xero and YHIL (was Re: Any non-Time
Warner characters in DC?)". <rec.arts.comics.dc.universe>, 1998/08/23,
via Google Groups.