Grubb was a male mole Dibbun of Redwall Abbey. Like all the other moles, he was very partial to raspberry cream pudding. He was also a good friend of Bagg and Runn. The trio got into mischief on a regular basis, much to the exasperation of their elders, especially Mother Mellus. At one point, wishing to be brave like Mariel Gullwhacker and Dandin, he ran out into the woods through the open wallgate, and was nearly kidnapped by two searats from the Darkqueen's crew, who were hiding outside. Unaware of their presence, he uprooted a small tree to use as a sword, and was severely chided for his actions by Mellus when she caught up to him. Her size and strength dissuaded the rats from attempting to kidnap Grubb, and they retreated without ever showing themselves.
When the army of searats attacked the Abbey in force, Grubb and his companions were confined to their dormitories. Once again, he managed an escape with the two otters in tow. The trio stole three of Friar Alder's best knives, and went up on the back wall of the Abbey, opposite from where the main fighting was going on, to play at being warriors. However, they discovered the wall was not deserted when ropes and grapnels started flying over the parapets, and decided, rather than warning the adult Redwallers, to simply use their pilfered weapons to cut the ropes before the rats could climb over. Grubb and the otters were chided for ruining the knives and sneaking outside, but were later hailed as heroes when it was discovered several searats died during the fall, and that the Dibbuns had averted what could have been a fatal ambush to the Redwall army.