Who is Gaspode from Men at Arms: A Novel of Discworld and what is their importance?

Gaspode the Wonder Dog is a magical accident wandering the city of Ankh-Morpork. He takes a liking to the werewolf recruit Angua and takes her under his wing, showing her the best places to get scraps, and revealing to her all of the ins and outs of gossip and hearsay that a mongrel mutt in his position has the opportunity to hear. Gaspode is remarkable for the fact that he can speak, and he is intelligent.