Django Wexler is the author of The Thousand Names and The Forbidden Library. At the Guardian, he shared a top ten list of animal companions in children's fiction, including:Bartimaeus from The Amulet of Samarkand by Jonathan StroudRead about the other entries on the list.
Bartimaeus is of course a demon – specifically a djinn – rather than an animal, but he spends a fair bit of time in the form of various creatures both real and supernatural. His snarky, sarcastic tone makes me think that he and Ashes would get along famously.
--Marshal Zeringue