"Be glad! The joy that we bring goes beyond mere sensory happiness. Yours is the privilege of assisting the Ssi-ruuk in liberating the other worlds of the galaxy." ―Standard greeting broadcast to planets prior to a Ssi-Ruuk invasion.[4]

The Ssi-ruuk (pronounced /'si ruk/),[5] Ssi-ruu in singular form, were a saurian species that invaded from the Unknown Regions of the galaxy and initiated the Invasion of Bakura in 4 ABY, shortly after the Battle of Endor. This race relied on a technology called entechment that involved extracting the life-energies of sentient beings and using them as power sources for their mechanical technology. They had a sizable war fleet and ruled an empire called the Ssi-ruuvi Imperium in the Ssi-ruuk Star Cluster near the galaxy's rim.

Ssi-ruuvi society was deeply compartmentalized—being dominated by a rigid caste system based on skin color which signified one's socio-economic standing. As a species, most Ssi-ruuk were xenophobic towards members of other species due to their stringent religious beliefs and the compartmentalized state of their society. Due to the remote position of their home territory in the Ssi-ruuk Star Cluster and their religious fear of dying on an unconsecrated world, few Ssi-ruuk traveled outside their Star Cluster. Thus, they remained largely unknown to the rest of the galaxy, and contact with outsiders was limited even in the days of the New Republic and the Galactic Alliance.

The entechment technology gets kind of low-key horrifying when Luke finds out he can "sense" the souls powering the drones with the force