Cold-blooded and utterly emotionless, the Psions were originally alien reptiles evolved to higher intelligence by Maltusian scientists. The Maltusians left their world to become the Guardians of the Universe and these creatures, who called themselves Psions, continued their evolutionary progress. Eventually the Psions traveled into space to find their creators. The Guardians, concerned with other matters, encouraged the psions to continue their quests for knowledge. The Psions, however, took scientific experimentation to the extreme, often selling their cruel services to other alien cultures. Psion research under the banner of the Citadel grave Tamaranean sisters K'oriand'r and Komand'r their star-bolt powers as Starfire and Blackfire. The Psions added their scientific savvy to the Dominator-led invasion of Earth, and engaged in breeding experiments that crossed humans with the H'San Natall to create young superbeings briefly united as a team of Teen Titans.
The Psions were part of the Earth Invasion. The Dominator's were afraid of the Earth's ability to create super powered indivuduals. Their contibution to the war effort was the creation of sedatives that would be given to prisoners in The Gulag that the Alliance housed in deep space. A science team based in conqured Australia sent a bomb through a JLI transpoter that backfired and killed the Psion science team. A psion was part of the Paradocs crew during Earths involvement of Our Worlds at War. He was tending a gravely wounded Wonder Woman and told her injuries were too far gone and he would begin dissection. Hippolyta took over taking care of her daughter's injuries.
The Psions maintain floating labs as they exploit the outer scientific fields of discovery. The Omega Men that are based in the Vegan system oppose them when they encounter each other.
The Goddess X'Hal was created through their experiments, The Green Lantern Corps were forbidden from entering this sector due to several ancient pacts with The Spider Guild and the Psions, as the official reason, and the being known as Agent Orange whos existence was known only to the Guardians. Kyle Rayner and Guy Gardner went into Vegan Space to save the life of Soranik Natu. The mission was a success leading to the defeat of The Spider Guild breaking most of the power they once had after attempting an invasion of Oa in retaliation.
The Omega Men are saved from Astrild Storm-Daughter by the Psions because the Psions wanted the Omega Men to assassinate Starro, Astrild's master. The Psions give the Omega Men Starro drones that they have experimented on. Through the experimentation, the drones' violet pigmentation converted to black and once the drones bond to its host, the host can appear as a Starro servant with augmented strength but the host still maintains their own free will. This will enable the Omega Men to get close to Starro and kill him.
Recently new depths to which the Psions would sink has been revealed through the Psion Green Lantern of sector 2828 (including the recently opened Vega system) called Gorius, as her and her sector partner came into conflict with the R.E.B.E.L.S. organisation, who were selling their sevices as a private security corp at the expense of the Green Lanterns, who were victims of a smear campain, having begun expanding into Vegan space, including New Tamaran. However Gorius recognized Starfire and despite the Tamaranians hated for Psions she sought her out as the Psions had hired the R.E.B.E.L.S. Leading Starfire to the artifical Psion-homeworld, Gorius showed Starfire to what was called a breeding-nexus an underground complex where Psion-females were kept as slaves, to produce a set number of male offspring with their guards. Gorius explained that the male Psions did this because the women still had the empathy the males lacked and would hamper their experiments if left free. Starfire was enraged at the treatment because it reminded her of her own time as a Prison prisoner and the two tried to free the captives, but the complex was destroyed from a far having been deemed an acceptable loss. Gorius didnt hear further from Starfire, but the princess forced Vril Dox to terminate the R.E.B.E.L.S. contract.