Mouse is one of a group of Temple Dog 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 Harry Dresden's car, the Blue Beetle, missing the flight back to Tibet and remaining with Harry during the events of Blood Rites. Dresden ultimately decides to keep the dog and names him "Mouse".
Mouse seems to possess an extremely high level of intelligence, able to formulate complex plans and understand instructions. He is a capable fighter and fast runner, and will occasionally emit a nimbus of pale light while in combat. His bark has the ability to break people out of an enchanted sleep and spur them to action. He also seems to possess an endurance and healing ability far beyond mortal dogs; a few hours after being hit by a car, he is able to fight a White Court vampire and his henchman.
Harry hung a tiny shield from his own bracelet on Mouse's collar so that he could track the dog should he ever need to.
Mouse liked going places in the Blue Beetle, he filled up the most of the back seat. It didn't matter that danger was where they were headed. For Mouse, it was all about the journey, not the destination. He also makes sure he has his own lead when he goes out with Harry or Molly. Harry suspects it's to make people feel more comfortable around a big dog safely tethered. — He's a people canine. 
In the seriesEdit
- Main article: Dead Beat
In Dead Beat, Mouse has grown a lot, now reaching up to Dresden's waist. Aside from being tall, he also has a broad build. Mouse's coat is dark grey, marked with black on the eartips, tail and lower legs.
- Main article: White Night
In White Night, when Anna Ash’s apartment building is on fire, and all of the residents were asleep because of a mild sleeping spell, and the Ordo Lebes women were trapped in Anna’s apartment due to a predator who's been stalking them is outside of her door laying wait—Mouse lets out with an extremely loud “WOOF” repeated over and over with mechanical regularity. The scale of it was similar to a Civil Defense storm warning. Harry describes it like a flood of sound, a solid living cascade that rattles your brain. All of the resident awoke and vacated safely without panic. The Ordo were able to escape with the evacuation.
- Main article: Small Favor
- Main article: Turn Coat
In Turn Coat, Mouse saves Molly Carpenter by putting himself between Molly and Morgan's bullet. She pulls it out, crying. As soon as Molly leaves the room, he's up and walking normally, faked it to make Molly feel her error more. As a Foo Dog, he's strong and probably didn't need the medical care. He saves her again when Peabody releases the Mistfiend at Morgan's trial when he's outed as the real murderer and the Council's traitor. 
Later, Mouse identifies Peabody as the the one who came through the Ways into Chicago. Ancient Mai declares Mouse a Foo Dog and therefore able to give testimony at Morgan's trial at White Council headquarters in Edinburgh, as did several of LaFortier's Asian supporters. Ancient Mai says, "Where did you get such a thing and why are you allowed to keep it?" To which Harry replies, "He sort of picked me."
- Main article: Changes
In Changes, a faint blue nimbus of light surrounds Mouse when he attacked the Ik'k'uox. The Ick threw Mouse by his tail, he hit the ground hard, letting our a cry of pain. Harry blasted the Ick with Soulfire saying “get off my dog”. Thomas comes to after his encounter with the Ick, then Thomas and Mouse team up. Thomas tells Mouse, "this time we do it smart", he'll get its attention so that Mouse can get its hamstrings. Faint blue light surrounds Mouse again and they take off zero to cheetah in a second—Mouse lets out a battle roar. Mouse is referred to by the Red Court vampires known as the Eebs as a "Mountain Ice Demon from the Land of Dreams".
While the fellowship is in hound form, Mouse talks to them and threatens to bite Lea's ass off if she doesn't change them back. She says he is far from his source of power, to which he replies that he lives with a wizard, "I cheat."
- Main article: Ghost Story
In Ghost Story, Molly told Harry that "Chewbacca is with her" meaning he's with with Maggie. Later, Uriel the archangel takes Harry to the Carpenter home where Mouse lives with Maggie Dresden referred to as "Little Brother" and reassured Harry that Temple Dogs have been known to live for centuries.
Several times during the series there are intimations of Mouse' divine origin. On occasion folks who understand Mouse' real nature are incredulous that Harry has him.
Word of ButcherEdit
- ↑ Jim Butcher Tweet
- ↑ Blood Rites, ch. 1 & 2
- ↑ Blood Rites, ch. 42
- ↑ 4.0 4.1 Proven Guilty, ch. 28
- ↑ White Night, ch. 25
- ↑ Dead Beat, ch. 3
- ↑ Changes, ch. 09
- ↑ Dead Beat, ch. 1: "My dog Mouse had started off as fuzzy little grey puppy that fit into my coat pocket. Now, almost a year later, I sometimes wished I'd sent my coat to the cleaners or something. Mouse had gone from fuzz-ball to fuzz-barge. You couldn't guess at a breed to look at him, but I was guessing that at least one of his parents had been a wooly mammoth. The dog's shoulders came nearly to my waist, and the vet didn't think he was done growing yet."
- ↑ Dead Beat, ch. 2: "The dog had been built on the scale of those statues outside Chinese restaurants, though—broad chested and powerful, with that same mountainous strength built into his muzzle. His coat was a dark and almost uniform grey, marked on the tips of his fuzzy ears, his tail, and his lower legs with solid black."
- ↑ White Night, ch. 12
- ↑ Small Favor, ch. 19
- ↑ Turn Coat, ch. 34
- ↑ 13.0 13.1 Turn Coat, ch. 47
- ↑ Changes, ch. 25
- ↑ Changes, ch. 41
- ↑ Ghost Story, ch. 11
- ↑ Ghost Story, ch. 50
- ↑ White Night, ch. 12
- ↑ Jim Butcher 2010 Bitten by Books Q&A