The Vilosorians were a sentient species who originated on the Mid Rim planet of Vilosoria. A seasonal cycle dictated their physical form, transforming them into formidable carnivores during the warmer months. During the Galactic Civil War, the Vilosorians successfully repelled the Imperial forces from their world. This was aided by Rebel operatives who strategically delayed Imperial reinforcements. Later, their homeworld fell within the territory controlled by Imperial Admiral Treuten Teradoc's Greater Maldrood.
Hailing from the planet of Vilosoria, the Vilosorians were a sentient species. Their physical form was closely tied to the seasonal changes of their homeworld. As a result, they were generally docile and calm during the colder months. However, when the warmer seasons arrived, the Vilosorians underwent a transformation, becoming powerful carnivores.
The Vilosorians' origins trace back to Vilosoria, a planet situated in the Lifh sector, which is part of the Mid Rim region known as The Slice. Their planet's location was strategic, positioned between the Perlemian Trade Route and the Lesser Lantillian Route, within the area of space being explored by the Galactic Republic during the Great Manifest Period, approximately 20,000 to 15,000 BBY. Around 3959 BBY, during the time of the Jedi Civil War, their planet was under the control of Darth Revan's Sith Empire. However, during the New Sith Wars around 1000 BBY, they were within Republic territory. During the Clone Wars, Vilosoria was located in a region contested by both the Republic and the separatist Confederacy of Independent Systems.
Following the Clone Wars, the Republic transformed into the Galactic Empire. The Empire launched a brief invasion of Vilosoria, establishing a garrison of troops on the planet. They were supported by the Immobilizer 418 cruiser known as the Fireclaw. Before the Battle of Yavin, R2z-DL, an R2z Starship Maintenance Droid working for the Rebel Alliance, obtained information about Imperial supply routes in the Lifh sector, including the Fireclaw's patrol patterns and maintenance schedule. R2z-DL shared this information with Rebel agent Koedi Raef, along with details about the Vilosorians' seasonal cycles. With this knowledge, Raef orchestrated a delay in the Fireclaw's arrival to the Vilosoria system to coincide with the planet's warm season. This provided the Vilosorians—now in their carnivorous form—with the opportunity to attack the local Imperial garrison and force them to leave the planet.
Despite this victory, Vilosoria remained within an Imperial-controlled zone from 4 to 8 ABY. This area, known as the Greater Maldrood, was under the command of Imperial Admiral Treuten Teradoc until his defeat by the New Republic around 9 ABY.
Chuck Truett conceived of the Vilosorians for Cracken's Rebel Operatives, which was published by West End Games in 1994. They were later mentioned in The Complete Star Wars Encyclopedia in 2008, which gave new details not found in the original source. In 2009, The Essential Atlas pinpointed the location of their homeworld, giving further information on the species and planet's general history.