What's black and white, obsolete, and goes "moof?" Clarus the Dogcow, of course!
Created in 1983 by Apple designer Susan Kare, Clarus was part of the original Cairo font. A sort of hybrid Holstein cow/dog, the dogcow icon was used in Apple printer setup dialog boxes for years to show the orientation of the paper -- the user could instantly recognize when the dogcow was right-side-up. The dogcow made another appearance in Apple's "Disk Copy" application during copies -- the dogcow wagged its tail and flipped over while the copy took place.
Apple issued official Macintosh Technote #31 in April 1989, further explaining the mysterious animal's history and habits. In the mid 1990s, Apple included the dogcow in its real-world Icon Garden -- by that time, the terms "Dogcow" and "Moof!" had been trademarked by Apple.
When Apple released Mac OS X, the dogcow was missing from printer dialog boxes, replaced with a sort of "Men's Room" stick figure. Users mourned the loss (including starting a petition to Save our Dogcow with over 8,000 signatures), and one developer fought back with ClarusX, a utility to reinstate the dogcow in printer dialog boxes...and thus, a lone "moof!" was heard echoing across the web.