In Garth Nix's Sabriel Trilogy, the Disreputable Dog is a powerful magical entity in the form of a midsize mongrel dog. the Dog is introduced in the second book, where Lirael, the lonely teenage mage creates a magical dog to befriend her. The spell that creates the dog takes on a life of its own, and instead of an unthinking dog image, Lirael creates a dog that is fully sentient and seems to be more than a simple magical talking dog.
As the story progresses, we learn that the dog is a mixture of Free Magic and Charter Magic, and has a great deal of magical power and understanding of cosmology, all while still having the attitude of a lazy, playful, somewhat naughty dog.
At the conclusion of the book, it is revealed that the dog is actually the fragment of one of the spirits that created the world, taking a last voyage in the world to set things to right. The dog is actually the essence of one of the spirits that created the Charter, but did not enter into it, which accounts for both its nature as being of both Free and Charter Magic, and for its disresputable, yet moral nature. In many ways, the dog seems to be a Trickster figure, in that she helped create the world, but does not seem to be bound by its rules, and seems to take a rather humuorous view of their sacredness. An interesting addition to Nix's cosmlogical mosaic.