The Chiss were a race of blue-skinned humanoids native to the planet Csilla, in the Unknown Regions. Their homeworld was locked in a planet-wide ice age many millennia ago, and they were forced to migrate away from the planet as a species in order to survive. They eventually returned to Csilla after colonizing more than two dozen neighboring star systems.
As a race, the near-human Chiss were well-muscled and tall, with jet black hair and glowing red eyes. Their skin ranged in color from pale to dark blue, depending on the amount of oxygen contained in the air they breathed. It was believed that their eye color was also enhanced by the presence of more oxygen in the environment.
Much of their history was marked by nearly continual warfare and conquest of other worlds, but the Chiss were generally not considered to be violent. Instead, their military doctrine was founded on a defensive posture that viewed the idea of a preemptive strike against an enemy as if it were murder. This unspoken law dated back nearly a millennium before the Battle of Endor, and was one of the strongest points of Chiss honor and morality.
Within Chiss society, children matured very quickly, never truly having an adolescent period before becoming adults. It was unclear if this was an evolutionary development, or simply a societal or cultural effect.
Like many races that inhabited the Unknown Regions, the Chiss remained ignorant of the rest of the galaxy. They developed interplanetary and hyperspace flight on their own, but never developed anything that resembled droid technology. Chiss society was based on the existence of several ruling families, which were represented on the Ruling Circle and oversaw the control of the Chiss Ascendancy. They jealously guarded their systems within the Unknown Regions, and openly sought out new territory to bring under their control.
Throughout their history, the Chiss repelled many invaders, although always after the invaders launched an initial against Chiss forces. Many of the scientists at the Astrographic Survey Institute believed that the Chiss were among the first races to come in contact with the Yuuzhan Vong, some fifty years before their initial invasion. They theorized that the Chiss understood the Yuuzhan Vong's military power, and began augmenting their own war machine to prepare to repel an invasion fleet. Unfortunately, the Chiss remained isolated in the Unknown Regions, and wouldn't allow contact with the New Republic after the Battle of Ithor. Chiss sages spent a great deal of time researching the Yuuzhan Vong, and eventually learned that it had taken the alien invaders many generations to cross the gulf between galaxies.