Apparently, an eating sequence Barks drew for «Interior Decorators» provided the inspiration for Gus' voracious appetite.
Gus' appetite not only provided a running motif to tie sequences together, it helped define his look. "Harry and I never really visualized Gus until we'd been using him in eating gags several times," Barks commented in April 29, 1987 notes. "Then we assumed he would have to be fat."
In Barks' hands, Cousin Gus acquired style and charm. Instead of being just a bloated nuisance, he became deft and imaginative in his eating habits, shuffling slices of bread and bologna like playing cards. In another gag, he cleverly steals a pea by sucking it through the spout of a teapot. Such unstoppable greed gives Gus a kind of strength: he is always able to outmaneuver Donald's attempts to protect his food.
Though Gus never returned to the screen, he became an established secondary character in the comics.