The Ur-Quan Kzer-Za are one of two subspecies created from the original Ur-Quan strain by the malicious Dnyarri. Nearly identical to their Kohr-Ah brethren, the most noticeable difference between their two is their skintones - Kzer-Za are green while Kohr-Ah are black. However, another difference is seen in their arms, where only Kohr-Ah appear to possess actual hands. At least part of their body is covered by a sheath which retracts when the creature experiences intense pain, along with the oozing of their talons.
The "Green Ur-Quan" are not natural. They were genetically engineered by the Dnyarri to serve as their "thinkers", to fill the roles of scientists, technicians, and overseers of the growing Dnyarri Slave Empire. Unfortunately for each of the new Ur-Quan subspecies, the genetic manipulation permanently divided them and exterminated the original species once and for all. The Dnyarri being as they were did not care to name either creation, and it was not until the slave revolt against their oppressive, mind controlling masters that this species named themselves after Kzer-Za, a hero who martyred himself to discover the secret to freeing their species from eternal enslavement.
During the time of the Dnyarri Slave Empire (20,000 to 17,500 BCE) it was Kzer-Za who found how to defeat the Dnyarri in discovering that the creatures would disconnect from a dying or seriously injured slave.
During the brief moments of lucidity that the Dnyarri gave their minions in the later part of their rule (probably out of laziness and complacency) Kzer-Za devised a plan. He waited until he was near a communication console and injected himself with a lethal dose of acidic poison. Before dying in agony he gained control of the device and broadcast his findings to every Ur-Quan on the planet.
That day the Slave Revolt against the Dnyarri began as Ur-Quan everywhere began hacking off their own limbs, stabbing themselves with broken glass and worse things. For every pain they inflicted on themselves, they were able to kill another Dnyarri, and the death of each Dnyarri would free more Ur-Quan. The blood bath continued until every Ur-Quan and every member of the former Sentient Milieu in the galaxy was free.
The name of Kzer-Za is legend among both Ur-Quan subspecies as a martyred genius. The Green Ur-Quan named themselves in his honor. His research also led to the invention of the Excruciator by the Ur-Quan, a violent device that is implanted directly into the brain and causes constant, horrifying pain.
From that day forward, the Kzer-Za would follow the Path of Now and Forever. This doctrine states that they must seek out all sentient (likely mistaken for sapient by the creators of the series, like most other Sci-Fi stories) life and offer them a choice: to either serve the Kzer-Za enslaved as a race of Battle Thralls or to be permanently imprisoned within a Slave Shield atmosphere dome through which there was no known escape. The Kzer-Za are aware that this way of life may be incorrect and so they willingly participated in the Doctrinal Conflict with their brothers, the Kohr-Ah, which began above the skies of the homeworld of their former allies, the Mael-Num.
For thousands of years they have circled the galaxy, enslaving sapient races into their Hierarchy of Battle Thralls or imprisoning them under impenetrable slave shields. Even one battle in their long history is an extreme situation in the eyes of a younger race. The Great War that most contemporary races speak of was, to the Kzer-Za, just another of a thousand conquests.
The Ur-Quan Kzer-Za go to war in their incredible powerful and intimidating Dreadnought starships, and for a time possessed a Precursor vessel known as the Sa-Matra.