The Falleen were a repto-mammalian sentient species who had a distinctive alien appearance. They were distinguished by their mottled green skin, ridged skulls, and their long, black hair which they typically wore in ponytails. Falleen exuded powerful pheromones which they used to attract mates.

Falleen were native to the planet Falleen, but were a colonial species who had migrated and adapted to dominate many worlds. and so also inhabited Ord Mantell alongside a human population.

During the Clone Wars, a cabal of Falleen nobles led the Black Sun criminal syndicate, which flourished while law enforcement declined as the Jedi focused on battling the Confederacy of Independent Systems. Black Sun became notorious in the lawless Outer Rim Territories and elsewhere, and its Falleen leadership operated out of a well-defended fortress on Mustafar. Xomit Grunseit led the cabal until Maul ultimately usurped control of Black Sun, and installed the leg-breaking lieutenant Ziton Moj as its ruler.

Black Sun was also involved in an underground dispute with the Pyke Syndicate, which led to Asajj Ventress and Quinlan Vos investigating a kidnapping by the Pykes. Ventress coerced a Falleen guard on Mustafar, leading him to believe his powerful pheromones had worked on her, and she and Vos strong-armed him into giving up information on the Pykes. The pair infiltrated the Black Sun fortress, fighting more Falleen to reach the kidnapped family.