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.