Who is Taggle from Plain Kate and what is their importance?

Taggle is Plain Kate's cat. Taggle is a normal cat at the beginning of the novel. However, when Linay grants Plain Kate her heart's desire in exchange for her shadow, her heart's desire is to have someone who will always be with her. This becomes Taggle. Taggle begins to speak and he is fiercely loyal to Plain Kate, doing all he can to protect her, even giving up his own life.