Dogs are a common animal in both the Muggle and Wizarding world, where they appear as mundane pets, formidable magical guards, and significant magical forms. They are featured as the Animagus form of a key character, a common form for the Patronus Charm, and the physical manifestation of a dark omen. Both ordinary and magical dogs play various roles throughout the Harry Potter series, from providing companionship to guarding powerful magical objects.
The most prominent example of a dog Animagus is Sirius Black, who transforms into a large black dog. This non-verbal, wandless magic allowed him to slip past the Dementors of Azkaban, as they could not sense his less complex canine emotions.
The dog is a known form for a corporeal Patronus.