The giant rat is a commonly featured animal in fiction stories, especially fantasy, where it is often a challenger that must be defeated by a hero. This scenario was parodied in the 1987 cult film The Princess Bride. The concept of giant rats is probably very old, but the most famous recent mention was in The Adventure of the Sussex Vampire, a 1924 Sherlock Holmes story by Sir Arthur Conan Doyle. In the story, Holmes says, "Matilda Briggs was not the name of a young woman, Watson, ...It was a ship which is associated with the giant rat of Sumatra, a story for which the world is not yet prepared." This cryptic reference spawned dozens of stories involving such a giant rat.
Actually, it turns out that there really is a giant rat living in Sumatra -- two, in fact -- Muller's Giant Sunda Rat, and the Mountain Giant Sunda Rat. These rats average about a foot in length, excluding the tail, and can weigh up to half a kilogram. In contrast, common rats are about half this size. The giant rats native to Sumatra are poorly understood, due to limited scientific study. However, surveys by the International Union for the Conservation of Nature have classified these animals as "Least Concern," indicating they are not endangered.
Rodents living in places other than Sumatra are sometimes mistaken as a "giant rat" due to their size. These include the capybara, the world's largest living rodent, and the Gambian Pouched Rat, which is the largest muroid (relative of mice and rats) in the world. The capybara, which lives throughout South America, can grow up to 4.3 ft (1.3 m) long and weigh up to 140 lb (65 kg). Capybaras have extremely efficient digestive systems and eat 6-8 lbs of aquatic grasses per day to survive. The Gambian Pouched Rat is about half the size of a capybara, with the largest individuals measuring about 2 ft in length. The Gambian Pounced Rat is native to Africa, where it is sometimes used to sniff out land mines. Due to its small weight, it can step over these mines without detonating them.