The Rancor is a fierce reptilian creature found in the Star Wars Universe. It is Native to the planet Dathomir. They are often captured and used as pets and mounts.
The rancor made it's sole film appearance in the Star Wars flims in Episode VI: Return of the Jedi. A pet of Jabba the Hutt, the crime lord uses the rancor as a means of execution via trapdoor.
Rancors have even been shown to inhabit the role of "vermin" albeit a dangerous one. in Star Wars: Knights of the Old Republic, a rancor has set up residency in the sewers. The player either fights the rancor or uses a thermal detonator and rancor pheromones to remove the problem.
Rancors have made appearances in many Star Wars video games, including Star Wars: Knights of the Old Republic, Star Wars: The Force Unleashed, and the expansion to Dark Forces 2: Jedi Knight - Mysteries of the Sith.