Mouse is one of a group of puppies believed to have Foo Dog ancestry, found and rescued by Harry Dresden after he was hired by the Tibetan monk, Brother Wang. The puppies are returned to the monk, but Mouse hides in Dresden's car, the Blue Beetle, missing the flight back to Tibet, and remaining with Dresden during the events of Blood Rites. Dresden ultimately decides to keep the dog and names him Mouse.
In the seriesEdit
Mouse starts as a puppy small enough to fit in a pocket of Harry Dresden's duster.(reference needed) He grows in size and power in the series, and by Changes he's assigned to Maggie Dresden as a support creature and bodyguard.
Word of JimEdit
[Mouse] does have a bunch of brothers and sisters who wonder how come they haven’t heard from him. ‘You never howl, you never pee on anything….’ And plus, there is…uh, I will just say that the possibility exists that Harry didn’t rescue all of them, and if so, where are the others?— Jim Butcher, noting that the evil sorcerer might still have one or more of Brother Wang’s puppies, leaving open a possible future meeting with Mouse’s "evil twin".Jim Butcher has stated that the breed that Mouse most closely resembles is the Caucasian Mountain Dog.[Footnote 1]
Jim has also noted that, though it may never come up in the series, Foo dogs traditionally draw their power from the threshold of their home, and that Mouse became much more powerful when he moved into the Carpenter household as a result. Mouse, he notes, had been forced to learn to draw from "other kinds of power" due in part both to Harry Dresden's tendency to flout convention and the comparatively weak threshold of Dresden's old apartment.