Gaspode is a small terrier-like dog featured in seven of Terry Pratchett's Discworld novels. He possesses human-level intelligence and the ability to speak, as well as an extensive collection of diseases (including 'Licky end' which is only found in pregnant sheep); he claims that the only reason the diseases haven't killed him is that they're too busy fighting amongst themselves to focus on him. However, since everyone knows that dogs can't speak, people tend to interpret his speech as their own personal thoughts, a tendency which Gaspode regularly uses to wrangle food from passers by. (In fact it has been mentioned in the books that a passerby kicked Gaspode into the gutter, and had gone no more than five steps before he thought "I'm a bastard, what am I"). The exceptions to this are Carrot Ironfoundersson (who eventually figures out the truth himself), Angua (whom he tries to court because she's a werewolf), the staff of the Times (whom he needs to pass some information to), and the Canting Crew (who believe in much stranger things than talking dogs). Gaspode's ability to speak also has uses against other dogs, particularly against the misanthropic Dog Guild in Men At Arms, shouting commands in human tongue (eg "Sit!", "Bad Dog!") that cause dogs to reflexively respond, in spite of better wishes. Gaspode frequently feels conflict between his desire to be a Good Dog and his belief that he has to look out for himself, because no-one else will. Despite being given a home with happy children and suchlike, he ran away from this for the life he's always known.
Gaspode originally gained his intelligence and ability to speak in Moving Pictures as the result of a "wild idea" which sought to (re)create a Discworld version of Hollywood. Descended from dogs that fled the destruction of the first appearance of this idea, Gaspode was "selected" to fill the movie role of the Wonder Dog. Unfortunately, he looks nothing like the common conception of what a Wonder Dog is, and so lost the position to Laddie (an obvious Lassie analogy), whereupon he became an agent for Laddie and the human actors Victor Tugelbend (renamed Victor Maraschino) and Theda "Ginger" Withel (renamed Delores de Syn). After the wild idea was contained/defeated, Gaspode lost the unwanted gifts that had been bestowed on him, and returned to being a homeless street dog.
In Men At Arms, Gaspode has regained his intelligence and speech as a result of sleeping too close to the High Energy Magic Building in Unseen University and being exposed to magical seepage. In this and the rest of the books he appears in, Gaspode is portrayed as something like a Dickensian urchin, scrambling to survive the harsh life of the streets while maintaining a lovable (if filthy) nature. Gaspode becomes the "thinking brain" dog (like a "seeing eye" dog) for Foul Ole Ron, and eventually joins the Canting Crew, a group of variably insane homeless people who have, as aforementioned, no difficulty in believing in talking dogs. Overall, within his disreputable appearance, Gaspode has acquired a survivor's intelligence that combines the street smarts of his upbringing with book smarts from reading badly-chewed-up books.
Gaspode also appears in the second Discworld game, Trouble with Dragons, which is largely based on Guards! Guards! but features Rincewind. He makes a small appearance at the inn where he gives the player trouble by using Rincewind like a doll and let him anger a nearby Sailor.
Gaspode enjoys using his powers of speech to antagonize Angua and poke fun at her. During the events of Men at Arms he often points out that Angua can not hide her attraction to Carrot from him because he can "smell" her feelings. In one instance, Angua is forced to change into a human with no clothes on, finding herself in Carrot's bedroom, Gaspode tells Carrot to "kiss her", prompting Angua to throw the luckless dog out of the room.
Gaspode is named after "the famous Gaspode", a dog who, upon his master's death, stayed at the graveside howling until he died (possibly because the gravestone was on his tail). This is a reference to Greyfriars Bobby.