Grainger is Ginny Johnson's West Highland Terrier dog. He only appeared in the Season 2 episode, A Dog's Life.
Schemer found Grainger so he could be a guard dog and later gave him to Dan, Becky and Kara they then gave it back to Ginny afterwards.
In the Season 3 episode, Billy's Party, Ginny mentioned that her dog had destroyed her Thanksgiving dinner, so Billy Twofeathers kindly gave her a ride to Dillylick to fetch a replacement dinner for the said holiday.