Delvin was a male mouse and a member of the Mouse Guard. A longtime friend of Rand's and a fellow shield bearer, Delvin chose to balance his defence with equal aggression. Delvin's generosity was well known throughout the mice of any patrol he had ever served in, and he often put the needs of any other mouse in his party above his own. On patrols, he carried a thick, short sword and his trusty, decorated shield.
During the winter of 1152, Delvin—alongside Aubrey, Bastian and Sienna—were sent to gather supplies from the northern settlements of Elmwood, Whitepine, Dawnrock, Thistledown, and Wildseed. Later that season, he attended Celanawe's funeral ceremony.
The following spring, Delvin and Bastian were sent by Gwendolyn to hunt down a snapping turtle near the settlement of Grasslake. While Bastian peppered the turtle with arrows, Delvin landed the killing blow with his sword.
- Delvin is the only known member of the Guard to have a fur cloak. Most Guardmice wear regular cloaks made out of cloth.