Jum Gurdy was an overweight, aging male otter Cellarkeeper of Redwall Abbey. He was also the brother of Dorka Gurdy, the nephew of Wullow, and the kin of Skor Axehound.
After Uggo Wiltud had a vision of Razzid Wearat and the crew of the Greenshroud attacking Redwall, he and Jum left the Abbey to find Wullow, who reportedly knew about Wearats. Jum later helped Uggo and another hedgehog named Posybud escape from Snaggs and his gang. Jum, Uggo, and Posy were separated while out on the sea. Jum met up with Skor Axehound's Rogue Crew and the Long Patrol, who informed him of the discovery of Wullow's body, after he had been tortured and (it was implied) burned to death by Razzid. Jum swore to avenge him, and accompanied them in their journey to warn the Abbey residents of Razzid.
Later on, the band encountered the aftermath of a bloody confrontation between the Guosim and Razzid's Crew. Some of the band, aided by the Fortunate Freepaws, stayed behind to help heal the wounded. Jum was one of these medics, but as soon as he was able to get away, he hurried to Redwall in pursuit of Razzid. He arrived just in time to see Razzid in the middle of a confrontation with Posy and Uggo. The female hedgehog stabbed Razzid with the Sword of Martin, but the Wearat refused to stop attacking even though he was wounded. Jum sneaked up behind Razzid and slammed his head with a large stick, crushing his skull and killing him, thus avenging Wullow's murder. Jum then took possession of the Sword of Martin from Posy and used it to help drive off the rest of the vermin. Afterwards, Razzid's ship Greenshroud was renamed the Posy Gurdy in his and Posy's honor, for slaying Razzid between them.