J'en was but one of hundreds of Green Martians forced into exile following the "Blue Inferno" event that eradicated all life on the planet Mars. She eventually immigrated to a world in the Cygnus system dubbed Mars II.
On Mars II, J'en met and fell in love with fellow Manhunter, J'onn J'onzz. However, when the ambitious soldier known as the Marshal staged a coup against the exiled Martian leaders, J'en decided to throw in with the Marshal. The Marshal proved to be extremely charismatic and J'en believed that he would lead the Martian culture to greater glory. J'onn obviously disagreed with the Marshal's initiative, and because of it, J'en and he were forced to go their separate ways. J'onn learned that the Marshal planned on invading and conquering the planet Earth. He fled Mars II in a shuttle, hoping to reach Earth in time to warn them. The Marshal sent a squad of hunter ships after him, and J'en was one of the pilots in charge of bringing J'onn down. Although J'onn reached the planet Earth, he was unable to prevent the a full-scale war between Earth's forces and the Martian fleet. During the war, J'en realized that she could not bring arms against her former lover, and she sided with him during the final battle between the Martian commander and J'onn J'onzz. When the Marshal was defeated, the remainder of the fleet agreed to return to Mars II. J'onn elected to remain on Earth, but J'en returned to Mars II with her people.
- Martian Physiology: The average Martian possesses the potential for the following power set:
- Shape-Shifting: Martians have psionic control of their physical for down to the molecular level. This allows them to a form of shape-shifting that allows them to mimic other forms, elongate aspects of their body, increase or decrease their physical size, and so on.
- Invisibility: Martians can cause the biopolymers in their bodies to lose their ability to reflect light, making the Martians invisible to normal light and human sight.
- Phasing: Martians can go through solid matter.
- Superhuman Durability
- Superhuman Strength
- Superhuman Stamina
- Extrasensory Input
- Super Hearing
- Martian Vision: Martian visual acuity greatly exceed human norms and allows for a wider range of information to be observed. This includes the following:
- Telepathy: Martians have the ability to read the minds of others and project their thoughts to varying degrees. They can also project their mental essences into a gestalt community known as the "Great Mind". Through this, the community can enhance the telepathic strength of other Martians. This power can also enable them to reverse the effects of amnesia or psychological brainwashing. 
- Astral Projection
- Mind Control: As an extension of this, Martians can also use the ability to alter a psychological profile of a target, enabling them to manipulate, and in some cases, outright control that individual. This practice is greatly discouraged however, and only rarely used. 
- Telepathic Relay
- Telepathic Assault
- Vulnerability to Fire: Martians are much more vulnerable to fire than the average Earth human. At times this has been portrayed as physical, psychological, or a combination of the two. The effect of this is to strip any Martian of their powers as they involuntarily lose control of their body.
- Battle armor
- Single-person Martian warship
- This version of J'en, 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.
- In Post-Crisis continuity, her counterpart is M'yri'ah, J'onn's wife.
- In Post-Crisis continuity, Martians do not have any body hair. In Pre-Crisis continuity, only the women typically had hair upon their heads.
- As many Martian names bear phonetic similarities to Anglican Earth names, J'en's name is likely pronounced "Jen", albeit with a distinctive dialect.
- Appearances of J'en (Earth-One)
- Images featuring J'en (Earth-One)
- Quotations by or about J'en (Earth-One)
- Character Gallery: J'en (Earth-One)