Centuries ago, Roh'kar and nine other Green Martians left their homeworld on a space-faring mission known as the Xendi Expedition. They launched shortly before the onset of the Martian Plague known as H'ronmeer's Curse, and thus survived the genocide of the Martian culture.
The craft carrying the ten Martian explorers crash-landed on Earth in a region of the Sonoma Desert in Arizona. Agents of the National Security Agency quickly converged on the scene and apprehended the surviving aliens, placing them within a special secret laboratory. Recognizing that they were Martians, the government scientists began performing experiments on them, in the hopes of developing a super-weapon. More specifically, they wanted to develop a process that could defeat Earth's resident Martian, J'onn J'onzz.
Although greatly weakened from the crash, Roh'kar and the others still maintained their native gift of telepathy. The other members of the expedition channeled their psychic energy into Roh'kar in the hopes of sending out a psychic S.O.S. The plan worked, and before long, J'onn J'onzz (better known as the Martian Manhunter) learned of their existence. He broke Roh'kar free of the laboratory and tried to get him to a safe-house.
NSA agent Rio Ferdinand used a brainwashed assassin named Paul Gerrard to track Roh'kar and his rescuer down. Armed with custom-made weaponry, Gerrard fired a fatal shot into Roh'kar's body. His dying words were a cryptic warning to J'onn in regards to the other members of his expedition. His body was recovered by NSA agents and used to to help develop Anti-Martian weaponry.
- 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.
- Roh'kar is based off of a Golden Age character named Roh Kar. Roh Kar was the first Manhunter from Mars, and made a single appearance in Batman #78 (two years prior to the introduction of J'onn J'onnz). The Golden Age Roh Kar is no longer considered part of modern continuity.
- Appearances of Roh'kar (New Earth)
- Images featuring Roh'kar (New Earth)
- Quotations by or about Roh'kar (New Earth)
- Character Gallery: Roh'kar (New Earth)