Roger the Mouse is a small white mouse that appeared in "The Lab Brat". In the episode, the mouse used by Daria for her maze experiment had no name, but in the fanfic "Scarlett", he turned out to be the reincarnation of Rita Barksdale's former boyfriend, Roger, who was mentioned in "I Don't" as having been killed in a skydiving accident. He became the talking companion of Scarlett and has reappeared, in both talking and normal-mouse modes, in other fanfics since then.

Roger the Mouse ("The Lab Brat")