From Monkey Island wiki
Steve Purcell was a graphic designer on The Secret of Monkey Island and Monkey Island 2: LeChuck's Revenge. His early influence in the games had huge lasting effects, for example in designing major characters like LeChuck and Guybrush Threepwood, using Deluxe Paint along with other artists to create the latter's character sprite, which was simply called "Guy" (as the character had no name at that point); Purcell later added "brush" to the file name, indicating that it was the Deluxe Paint "brush file" for the "Guy" sprite. The file was then saved as "guybrush.bbm", so the developers eventually just started referring to this unnamed 'Guy' as "Guybrush". Purcell is also the creator of the comic book characters Sam & Max. As a tribute those two characters have appeared in the first four Monkey Island games in one form or another.