Saturn was once inhabited by two humanoid races, red skinned desert Saturnians, and the white skinned polar Saturnians, who mistrusted one another for centuries. During the reign of king Jaxx, the simmering feuds became a full scale war.
Jemm, the red skinned son of Jaxx, was born with a birthstone on his forehead and was believed to be the savior promised by Saturnian religion. As a child, Jemm escaped the destruction of Bhok. Later, due to a nuclear accident, all life on Saturn was thought to have been wiped out. However, Jemm, his mother Jarla and his teacher Rahani were saved. After Jarla and Rahani died, Jemm went to Earth.
Creators Greg Potter and Gene Colan had Jemm, Son of Saturn originally created for the maxi-series as Jemm, Son of Mars and was to be the cousin of the Martian Manhunter and fellow green-skinned Martian at a time when Martian Manhunter was not making any appearances. When it was learned that the Manhunter would return to the Justice League, Jemm was reworked as being a red-skinned alien from Saturn and the appearances by the Manhunter was changed to his cousin Joggar.
Later, writer John Ostrander, in an attempt to explain the similarities between the aliens of Saturn and Mars, created the back story that the Saturnians were clones of the Martians from long ago, and that the use of the clones as slaves by the White Martians had lead to a civil war.
Interestingly, a red-skinned alien from Saturn had appeared in a Martian Manhunter story back in April 1963's Detective Comics #314.
Major Story Arcs
Once on Earth, Jemm was taken captive by Synn, one of the few remaining white Saturnians who had always sought to wipe out their red counterparts. Jemm escaped to new Bhok, where the remaining Saturnians lived. Aided by Earthmen Claudius Tull, Synn attacked New Bhok. Jemm, believing he should protect all Saturnians, prevented the Reds from wiping out the Whites.
But then Claudius Tull, having been transformed into a mighty being of pure energy, tried to wipe out the Saturnians. Before he was stopped, partly due to Jemm's efforts, Tull had killed most of the white Saturnians. Jogarr forced Synn to surrender. Jemm, knowing he was hated by both Red and White Saturnians chose to return to Earth.
Years later, during the Rock of Ages storyline, Jemm was unwilling controlled by Lex Luthor and the Injustice League with the Worlogog. After being freed by the JLA, Jemm's mind was weak and damaged, so J'onn J'onzz took responsibility for his care. He revealed that the Saturnians were created by the Martians in their image but modified to be best suited for Saturn. J'onn felt responsible for J'emm just as the Martians were responsible for the Saturnians. While under J'onn's care J'emm was tortured by Ma'alefa'ak, J'onn's evil brother, taking on J'onn's form to discredit the Manhunter from Mars.
In the story arc Rings of Saturn he returned to Saturn to take part in an arranged marriage with Cha'rissa to unify the Red and White Saturnians. They then took the throne as leaders of all of Saturn.
Jemm later made an appearance in New Krypton, where he voiced his protests over the Kryptonians moving one of Jupiter's moons, Callisto, without concerns over other beings living in the Solar system. He was also furious at the Kryptonians' relations with the Thanagarians, whom he sided with the Rannians against in the Rann-Thanagar War, and he considers to be bloodthirsty war mongers. He stormed into the chambers of the council, and when they would not hear him, sought some more drastic measures, which soon escalated into a full-blown battle. Fortunately, Superman was there to calm both sides before any bloodshed took place. Jemm left Krypton, confident that he left a powerful message on the high council. Before he left, he did take time to pay respect to the Kryptonian deity, Rao.
Jemm is shown to still be the leader of all the races living on Saturn and its moons now, including the people that Saturn Girl will descend from.
Powers and Abilities
A Red Saturnian, Jemm is a powerful being, capable of engaging Kryptonians and Martians in a physical fight in terms of raw strength. He also has limited shape shifting abilities, which he can use to stretch his form.
In addition to this, Jemm is powerful telepath, and is capable of firing telepathic energy bursts from the organic gemstone situated on his forehead. This gem is called "Mark of Jargon."
Jemm is capable of rapid cellular regeneration.
Jemm can fly and is capable of surviving in space indefinitely.
He has a weakness to fire, a trait inherited from Saturnians Martian ancestors.
In the reality of Flashpoint, it was revealed than Jemm is a pivotal part of Amanda Waller's Task Force X, where he serves to control the whole army of superpowered metahumans, most of them dangerous criminals, to serve as an army against the amazon forces of Wonder Woman.
In the Black Label series Superman vs Lobo, after Lobo gained the means to alter time and space, he created an altered reality where Jemm was member of the League of the Last Sons, a team composed of the last survivors of different alien species and under the leadership of MainMan, the altered identity of Lobo, they protected Earth.
In Other Media
Jemm appeared in season one episode seven of Supergirl. Jemm was a prisoner of the DEO who escaped, and forced Hank Henshaw to reveal himself as the Martian Manhunter to Alex Danvers.