Jes-Mo was a native of the city of Kandor on the planet, Krypton. In Kryptonian year 9846 he served as chief scientist under General Pir-El in the waning days of the Last War. After the nation of Erkol devastated the city of Kryptonopolis with a solar-powered robot ship, Pir-El instructed Jes-Mo to design a device that could counter the solar-ship's capabilities. He invented a missile which emitted a thick, black chemical cloud, blocking solar radiation thus disabling the Erkol robot ships. Jes-Mo's invention proved to produce an unexpected (yet serendipitous) side effect however. As the black cloud descended upon the warlords of Erkol, a chemical reaction altered their personalities to such an extent that they adopted a more passive attitude and elected to make peace with their rivals in Kandor.
Jes-Mo possessed no superhuman powers while living under a red sun. Had he existed on a world revolving around a yellow sun, he would have developed physical attributes equal to those of Superman.
- This version of Jes-Mo (Earth-One), including all history and corresponding appearances, was erased from existence following the collapse of the original Multiverse in the 1985–86 Crisis on Infinite Earths limited series. Even though versions of the character may have since appeared, this information does not apply to those versions.
- Jes-Mo's final fate has never been revealed, but it is reasonable to assume that he passed away of natural causes long before the ultimate destruction of Krypton.
- 1 Appearances of Jes-Mo (Earth-One)
- 1 Images featuring Jes-Mo (Earth-One)
- Quotations by or about Jes-Mo (Earth-One)
- Character Gallery: Jes-Mo (Earth-One)