Rancors were large carnivorous reptomammals native to the planet of Dathomir. They were usually born brown, but in special circumstances, such as the mutant rancor, jungle rancor, and the bull rancor, their color may have differed. Although found on other worlds such as Lehon—where they were brought by crashed starships—Ottethan, Carida, Corulag, and Felucia, those from Dathomir were said to be stronger and more intelligent than others. They had been used for many things, ranging from mounts for the Witches of Dathomir, to pets for crime lords such as Jabba Desilijic Tiure, to being a source of food, and as a means of entertainment by dropping someone into its pit.

Vonnda Ra of the Nightsisters used a stuffed rancor head as a chair. In her youth as a Jedi trainee, Hapan Queen Mother Tenel Ka Djo used two trophy rancor teeth for handles to create both her first lightsaber and second lightsaber. Rancors were also the source of the delicacy (or at least an edible meal) known as raw rancor-beast liver.

The concept for the rancor in Return of the Jedi was described by its creators as «a cross between a bear and a potato.» It was first to be played by an actor in a suit, but no one was satisfied with the results. The rancor was then made as a rod-operated puppet, filmed with a high-speed camera to slow its movements down to give the illusion of a much larger creature.^[21] A combination of matte painting, cartoon rotoscoping, and CG elements were added around the creation to make it look bigger and more menacing. Some of these changes were later omitted or replaced with CG effects in the 2004 DVD release of the original trilogy.

In contrast to the rancor’s classification in other sources, Star Wars Galaxies states they’re a hybrid of a crustacean and an arachnid.

Ben Burtt, sound designer for all seven movies, said in the Galactic Phrase Book & Travel Guide that he created the rancor’s sounds from those of a dachshund.