Together with General Zod, Jax-Ur attempted to re-establish Krypton on Earth by bringing about a terraformation apocalypse (in the Black Zero Event), but he was ultimately defeated by Superman and re-imprisoned in the Phantom Zone.
After Krypton was destroyed, Jax-Ur, and all of the other prisoners in the Phantom Zone were freed. He subsequently joined together with General Zod and his forces. They then use the ship they were aboard and travelled across space, searching for other Kryptonian survivors, before finding Kal-El on planet Earth.
After Superman and Lois Lane were brought aboard Zod's flagship, the Kryptonian atmosphere inside negates his powers. Superman was strapped down and General Zod had Jax-Ur conduct mind probing for information, before General Zod proceeded to Smallville to retrieve the Codex.
After General Zod and his forces return to the ship from battling Superman and the US military, Jax-Ur notified General Zod that he had located the Codex, telling him that Jor-El had disintegrated it and combined it into Superman's DNA. He also boasts that he can extract it from Superman, dead or alive.
Jax-Ur is later sucked back into the Phantom Zone (along with Faora, Nam-Ek, Tor-An, and Car-Vex) after Nathan Hardy piloted a plane with Superman's ship inside into the Black Zero, causing a temporary energy singularity into the Phantom Zone (due to the collision of both Phantom Drives).
Genetically engineered into the Kryptonian Thinker Guild as a scientist, Jar-Ur is extremely intelligent, but unlike his compassionate fellow scientist Jor-El, Jax-Ur is cold and cruel, as he had no qualms about experimenting on a restrained and helpless weakened Superman, due to his determination to discover the Growth Codex for General Zod.
- Genius-Level Intellect: Jax-Ur, while not on par with Jor-El, is nonetheless exceptionally intelligent, as a member of the Kryptonian Thinker Guild, with his intellect mainly extending to his scientific expertise. He occasionally offered crucial insights to General Zod, which helped the Sword of Rao survive for so long after Krypton's destruction. However, the thinking boundaries programmed into Jax-Ur's engineered DNA occasionally make him imperfect in utilizing these skills, being therefore notably less intelligent than the more free willed Jor-El.
- Expert Scientist: Jax-Ur, as an illustrious member of the Kryptonian Thinker Guild, was one of Krypton's foremost scientists, almost on par with Jor-El. It was under Jax-Ur's instructions that General Zod was able to retrofit the Phantom Zone Projector into a Phantom Drive, to use for searching the universe for other Kryptonian survivors. After examining Superman blood, Jax-Ur was also the one to discover that the Growth Codex had, in fact, been fused with all of Kal-El's cells. He also swiftly understood how the Earth's sun granted Superman superpower. Finally, Jax-Ur was the only member of the Sword of Rao to understand that the Phantom Zone energy singularity had been opened due to the collision of both Phantom Drives.
- Multilingualism: Jax-Ur, apart from his native Kryptonian, was somehow able to quickly learn how to fluently understand and speak English (and possibly other Earth languages), as seen during his brief interaction with Superman.
- Space Suit: Jar-Ur wears this protective suit in airless or otherwise dangerous space environments, notably when on the Daxam colonial outpost.
- Syringe: Jax-Ur's syringe of Kryptonian design, used to extract Superman's blood.
- In the DC Comics universe, Jax-Ur was a scientist imprisoned in the Phantom Zone for destroying Wegthor, an inhabited moon of Krypton.
- Jax-Ur is the only known member of the Sword of Rao not to have been from the Kryptonian Warrior Guild, as he was from the Thinker Guild instead.
- In Smallville continuity, Dax-Ur (also from the House of Ur) was a kryptonian scientist that came to Earth in order to explore the effect the yellow sun has on kryptonian minerals, coincidentally discovering its effect on kryptonians. Decades later, the 22 year old Clark Kent tracked him down and asked for his help in defeating Bizzaro (a mutated kryptonian experiment that metabolized kryptonite and was weakened by yellow sunlight). Dax-Ur gave him Blue Kryptonite (that painlessly suppresses the kryptonian ability to metabolize solar radiation, practically rendering them human) that he used to overload Bizzaro's body and caused him to explode.