Capybara

The capybara, Hydrochoerus hydrochaeris, the world's largest rodent, lives in South America and Panama. It is the only species in its genus, which belongs to the family Hydrochoeridae, order Rodentia, but different rat class and rat species. The capybara, also called carpincho and water hog, has a massive body, a large head with a blunt snout, short legs, and a very small tail. It may weigh as mush as 50 kg (110 lb) and have a shoulder height of 50 cm (20 in) and a body length of 130 cm (51 in). Its hair is coarse, reddish brown and armed with strong claws. Capybaras eat only plants. They are fast runners and swim well, even under water.

The docile capybara, which may grow to the size of a sheep, is the largest rodent in the world. So the biggest rat in the world that many describe on the web or blog may not the real rat like this one, because many kind of rodent that resemble with rat but actually just other rodent type.