Crumdun was a fat, cheerful stoat in the crew of Razzid Wearat who had suffered many head wounds in fights. As a result, he was not very bright. He was described as Braggio Ironhook's constant shadow, following the big ferret around and supporting his deeds, though often trying Braggio's patience with his stupidity.
After Braggio was slain by Razzid, Crumdun pretended to side with the Wearat and sailed with him aboard the Greenshroud; in truth, he was saddened and horrified by the beheading of his messmate. During the voyage, the other vermin teased Crumdun for his slowness, until he decided he had taken enough and deserted the ship.
Wandering the dunes, Crumdun was taken captive by the Long Patrol, but they treated him quite well once he agreed to help them. Crumdun provided the hares with all of the information that he could, traveled with them, and began to rather enjoy their company. However, when the Long Patrol joined forces with the Rogue Crew, the hostile otters refused to believe that a vermin could have told them everything without holding something back and tortured him. Sergeant Nubbs Miggory stepped in and saved Crumdun's life. However, fearing that he would eventually be killed by the vermin-hating sea otters anyway, Crumdun contrived an escape. Deciding that he didn't want to be big and tough like Braggio after all, Crumdun resolved to live out his days alone in peace. He and Voogal were the only members of Razzid's crew to survive.