The history of Clarus the dogcow: The dogcow (actually it was just a dog at this point) first appeared in the font called Cario which was part of the original verson of the Macintosh Operating System. It was drawn by Susan Kare who, among other things, also drew the trash can and the watch pictures used in the original OS.

About the time that the Cairo font was being phased out and after Ms. Kare had left for NeXT the Apple team needed a picture for their Page Setup dialog box that would illustrate how the page was going to be oriented when it was printed. The dog from the Cairo font fit the bill. It was blown up and put in the dialog. However, the dog didn't survive the translation well. As a matter of fact, a debate arose as to whether the picture in the dialog was a dog or a cow. Eventually, to settle the matter, it was branded (no pun intended) a dogcow.

At least that's one version of the story. As is true with much of Apple lore, there's more than one way the story gets told.