The Kryptonian citizen registry growth codex (or simply the codex) was the remains of an ancient Kryptonian that contained the potential genetic information of Kryptonians to be used in conjunction with Kryptonian genesis chambers.
The codex once belonged to an ancient Kryptonian with whom modern Kryptonians shared an identical genetic makeup. Kryptonian society developed the technology to read and later implement the genetic sequences of the remains to fetus models so as to establish artificial population control, thus producing citizens fit for a predetermined role in Kryptonian society upon birth.
During the era of Kryptonian expansion, with a massive terraforming project underway to spread their influence throughout the galaxy, genesis chambers were created for Kryptonian scout ships so they could carry embryos to new worlds for colonial repopulation.
Prior to Krypton's destruction, Zod organized a radical coup d'état to overthrow the Kryptonian Law Council with the paramilitary faction known as the Sword of Rao, with the intention of bringing order to their failing society. Zod attempted to seize Kandor's main growth codex with the intention of purging any bloodline deemed weak in hopes that the movement would cause a restorative effect to the race and their dying planet.
However, Jor-El, Zod's life-long friend, immediately opposed this ideology and, after escaping arrest, stole the codex in order to bond the genetic information within to his newborn son's cells to be sent off to a distant planet so as to preserve Krypton's legacy. Zod's revolution was quickly ended and he, along with all of his radicals, were sentenced to three hundred cycles of somatic reconditioning within the Phantom Zone for crimes against the state and the murder of several government officials including Jor-El and High Eminence Ro-Zar.
After the planet's destruction, the Sword of Rao members were liberated from the Phantom Zone due to the surge of energy released. Tirelessly, they journeyed through space in search of survivors before receiving a distress signal from an ancient scout ship located on Earth, inadvertently activated by Kal-El during his reunion with his father's consciousness.