From The Essential Jack Ziegler (see here), editor Lee Lorenz speaking, four pages on the nature of cartoons, with examples of Ziegler alluding to comic strip characters (Superman, Mickey Mouse, the Lone Ranger, Flash Gordon, Archie):
Cartoon is definitely not a portmanteau word, in the sense that portmanteau has in linguistics, and its etymology isn’t very complicated. From OED2:
< French carton or (its source) Italian cartone, augmentative of carta paper
What makes cartoon like the suitcases called portmanteaus is that it covers lots of different things, from commercial ads through graphic novels, just as the suitcases can contain many different things.
There’s a lot of passing back and forth between cartoonists — all the time in Bill Griffith’s Zippy, and every so often for some others.