The Evocii are a primitive humanoid race from Nal Hutta, formerly Evocar. When the Hutts arrived on Evocar, the Evocii were amazed by the technology these large, fat slug-like aliens brought with them and began swapping areas of their own home world for the technology that the Hutts had.
Soon they realized that the Hutts owned almost their entire world and then the Hutts began treating the Evocii like slaves. The Evocii appealed to the Galactic Republic for help but unfortunately, the laws of the Republic favored the Hutts.
Eventually the Hutts brutally relocated the Evocii to Evocar's fifth and largest moon Nar Shaddaa, where they were used as slaves to build Nar Shaddaa into a spaceport moon. Most of the Evocii eventually died from the various technologies practiced on that moon while the very few survivors deteriorated into savages.
The ancient history of the Evocii tells that their people revered a holy stone, known as the Uransien. Supposedly this spherical stone watched over the people, and as long as it rested peacefully within the Evocii capital, the people enjoyed good health and prosperity. After the Hutts invaded, however, the Uransien was lost. This may have been a factor in the speed of the Evocii's despair.