Grubbage was a large, fat, mostly deaf wharf rat in the motley crew of the Seascab, serving as the bosun and the steersrat. He was, according to Malbun Grimp, jolly and likeable, and an excellent navigator.
Due to missing both ears, Grubbage often misunderstood what his crewmates said (a fact that constantly irritated his captain, Plugg Firetail, and provided comic relief). However, he generally figured out any commands a little while later.
Grubbage and Scummy reattached Plugg's tail with pine resin after it was shorn off. Both corsairs had to walk behind him to make sure his repaired tail did not fall off.
He was captured by the Redwallers in Mossflower Woods near Brockhall. However, they liked him, and he was taken inside Redwall Abbey. Grubbage helped navigate Triss and her friends to Riftgard, after which he presumably returned to Redwall. There he was popular and liked by all; it is presumed he stayed there until the end of his days.