The Growth Codex, simply known as the Codex, was a skull that contained the genetic information of the entire Kryptonian race.
Presumed to have belonged to an ancestor of the Kryptonian race, the Codex was used to analyze certain pieces of genetic code and use it so that newborn babies would have a predetermined societal role. Although there's no certainty, the artificial population control is believed to have caused a good deal of controversy.
Thousands of years later, a terraforming project was initiated in an attempt to spread the Kryptonian race throughout the universe. Genesis Chambers were created on scout ships in order to populate new worlds.
Sometime before Krypton's destruction, Dru-Zod staged a coup d'état in an attempt to seize the Codex and eliminate any "degenerate bloodlines." His childhood friend Jor-El, managed to steal the Codex and bond its genetic information with the individual cells of his newborn son Kal-El. The baby was then sent to Earth in an attempt to preserve Krypton's legacy.
Following the planet's destruction, Zod and his surviving followers set out to find possible survivors and obtain the Codex. After receiving a distress signal from Earth, which had been inadvertently activated by Kal-El, they attempted to terraform the planet into a new Krypton but were ultimately defeated.
- Though never stated, the Codex's capabilities resemble Kandor due to the fact that they both were used to bring deceased Kryptonians back from death and create a new Krypton.