The Ssi-ruuk were warm-blooded, reptilian beings native to the Unknown Regions planet Lwhekk. They were covered with scales of various colors. Their blunt, oversized heads ended with a beaked mouths, and their bodies were balanced with muscular tails. They had clawed hands and feet, and strongly-muscled hind legs. Each hand had three opposable digits. Because of their reptilian ancestors, the Ssi-ruuk had three eyelids that provided varying levels of protection from light.

The Ssi-ruuk were blind to the Force, and communicated with each other via a complex series of tweets and whistles. They also had scent tongues which they ejected from their nostrils, giving the average Ssi-ruu an incredible sense of small.

As a rule, the Ssi-ruu were highly xenophobic, but were more disgusted by other species than afraid of them. In general, a Ssi-ruu avoided personal confrontations, and would never fight on planet that had not been properly consecrated, for fear of dying without the ability to reach the afterlife.

There were at least four races of Ssi-ruuk, based on their coloration. They held to a very rigid code of honor, as defined by the G'nnoch, and their strict caste system was based on skin coloration and patterning. Blue Ssi-ruuk were members of the highest caste, and were the politicians and leaders of their society. Gold-skinned Ssi-ruuk were very rare, and were members of the religious caste. Red Ssi-ruuk were generally stronger than their counterparts, and comprised the military caste. The green-scaled Ssi-ruu were workers. Brown-scaled Ssi-ruuk were usually the offspring of mixed or unsuccessful breedings, and were often killed at birth. Rarely, a black-scaled Ssi-ruu was born, and was taken aside for training as an assassin or bodyguard to Ssi-ruuvi leaders.

As a people, the Ssi-ruuk were also highly religious, as evidenced by the power of the Conclave in governmental decisions. As has been noted, they feared the possibility of dying away from their homeworld, believing that the soul of an individual who died on another world would be lost forever. Thus, the Ssi-ruuk consecrated every world they wanted to colonize, to ensure there was an afterlife for their souls.

Legend held that a Ssi-ruuvi individual would be born with all colors on their scales, a rainbow-scaled individual known as the Keeramak. The birth of the Keeramak would signal the end of the caste system, allowing the weak and oppressed castes to become leaders. Such an individual was born just prior to the Yuuzhan Vong invasion. However, this individual was not a messiah, but the pawn of a Yuuzhan Vong invasion force that was trying to capture Lwhekk and Bakura, thereby establishing a foothold along the borders of the Unknown Regions. The Ssi-ruuk were then subjugated by the alien invaders, and forced to play their part in the plan

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