The Terrible Dogfish

The Terrible Dogfish () is a dogfish-like sea monster, which appears in Carlo Collodi's 1883 book "The Adventures of Pinocchio" ("Le avventure di Pinocchio"). It is described as being larger than a five-story building, a kilometer long (not including its tail) and sporting three rows of teeth in a mouth that can easily accommodate a train. So fearsome is its reputation, that in Chapter XXXIV, it is revealed that the Dogfish is nicknamed "The Attila of fish and fishermen" ("L'Attila dei pesci e dei pescatori").
In the novel.
The Dogfish is first mentioned in Chapter XXIV, when Pinocchio, searching for his creator, Geppetto, is informed by a dolphin that he has likely been swallowed by the Dogfish which "...for some days has come to wreak extermination and desolation in our waters". The Dogfish is later mentioned in Chapter XXVI by Pinocchio's school friends on the Island of the Busy Bees ("Isola delle Api Industriose"), who tell him that it has been sighted on the coast, to coax him away from school.
The Dogfish makes its first appearance in Chapter XXXIV when Pinocchio, recently transformed from a donkey to his puppet form, has entered the sea to escape from his former owner. The Fairy with Turquoise Hair, in the form of a mountain goat, warns him of the Dogfish too late, and it swallows him whole, along with a tuna whom he befriends. He discovers Geppetto, who reveals that he has been trapped inside the Dogfish for two years, surviving on ship supplies swallowed by it. When it is revealed to suffer from asthma, a condition that forces it to sleep with its head raised from the water and its mouth open, Pinocchio carries Geppetto on his back and swims out of its mouth. When Pinocchio's strength begins to fail, the tuna helps them reach the shore.
Disney version.
In the 1940 Walt Disney film "Pinocchio", the Dogfish (named Monstro, Portuguese, Esperanto, and archaic Italian for 'monster') is portrayed as a terrible giant whale with massive jaws, both of which have sharp teeth, and a grooved underside like a rorqual. He is first mentioned in a message from the Blue Fairy about Geppetto, who, sailing to find Pinocchio, has been swallowed by him. They search for him, but are frustrated by the fear the various nekton display at the mention of his name. After finally discovering him sleeping, he suddenly awakens and swallows Pinocchio, who discovers Geppetto in Monstro's throat. There, Pinocchio frees them by starting a fire, the smoke of which prompts Monstro to sneeze them from his mouth, whereupon he gets angry and pursues them, but fails to kill them and, when Pinocchio pulls Geppetto into a cove, Monstro smashes against the rocks surrounding it. 
Monstro was animated by Wolfgang Reitherman, the go-to man for action sequences among Disney's Nine Old Men. His growls (though uncredited in the film) were provided by Thurl Ravenscroft. In ABC's "Once Upon A Time", Monstro makes a brief appearance in the episode "The Stranger", in which his Disney role is reiterated. Monstro's design has many similarities to the Devil Whale found in various other tales.
In "Kingdom Hearts".
Monstro also appears in the video game "Kingdom Hearts" as both a supporting character and a world, where Pinocchio and Geppetto temporarily live inside him until being rescued. Within Monstro dwell many Heartless, including one called the Parasite Cage, which traps Pinocchio in its cage-like stomach, and delivers him to Riku, who wishes to use his heart to rescue Kairi. After Kingdom Hearts is sealed, Monstro presumably returns to his world. 
He later reappears in ', as a figment of Sora and Riku's memories. He is not physically seen, but card rooms resembling his bowels are explored. In the "Final Mix" version of ', Monstro appears as a boss fight in the Mirage Arena. He reappears as a sub-world in his homeworld, Prankster's Paradise, in "".
In "Bonkers" (TV series).
Monstro makes a guest star appearance in a "Bonkers" comic story titled "Whale of a Tale", published in the December 1994 issue of "Disney Adventures". In this story, he is a polite actor playing a role in "Pinocchio", who has not found work in the movies since then; he is duped by a gang of crooks, posing as a movie company, into breaking into banks for them to rob, and upon finding out the truth, helps Bonkers catch the criminals.
In "Fantasmic!".
Monstro also plays a notable role in the Disneyland version of Fantasmic!, and also has a smaller role in the Dancing Bubbles scene in the Disney's Hollywood Studios version.