As Dr. Simon Jones he was working on making contact with other dimension until he was contacted by Trigon who used his abilities to turn Simon into a powerful psychic that goes by Psimon.
Dr. Simon Jones was working on interdimensional experiments when he met Trigon the Terrible, Raven's demonic father. The demon changed Jones into the villain known as Psimon and gave the transformed scientist a mission: destroy the world. While reading a classified ad in the Underworld Star, he saw the perfect chance to form a team and fulfill this mission.
Biding his time, Psimon tolerated the buffoonish Dr. Light's leadership, then finally seized power, taking over the reins as head of the Fearsome Five. Psimon was arrogant, power-hungry and smug in his powers. He was an excellent tactician who spoke with grandiose verbiage. He did not always kill his victims, preferring to instill his opponents with fear of himself and his mental powers.
Psimon eventually became part of the Monitor's advance team during the Crisis. Psimon tried to take the leadership of the villain army away from Lex Luthor and was killing him until a blast of energy from Brainiac smashed open Psimon's brain dome, apparantly killing him.
But Psimon was somehow able to survive the experience, and resurfaced much later. He cut a swath of destruction through a star system, devastating the planets of Kallas and Talyn (home of Jarras Minion). Eventually, Psimon returned to earth, where he sought for revenge against all those who wronged him, including his former teammates.
Psimon viciously attacked Mammoth, Shimmer and Gizmo, attempting to kill them all. Psimon savagely attacked the Mammoth and Shimmer - driving a spear through Baran's head. He then transformed Selinda into glass and shattered her. Next was Gizmo: Psimon used his powers to continually shrink Gizmo - until he reached the subatomic level.
Psimon then attacked the Titans, and psychologically tortured each of them, while also unwittingly unlocking new abilities in the Titan, Mirage. Jarras Minion arrived on earth on a mission of vengeance. Minion intended to kill Psimon, who destroyed his planet. With Mirage's new abilities and the arrival of Minion, the Titans were able to contain Psimon. The dangerous villain was placed under custody of the Darkstars.
Sometime later, Psimon was remanded to the Slab , a super-high-tech prison which hosted a variety of super-powered inmates. When Brother Blood attempted to activate a global satellite-activation system, Psimon used the opportunity to initiate a major prison breakout at the Slab. Psimon, along with hundreds of other inmates, escaped while Nightwing and the Outsiders were preoccupied with Brother Blood's plan.
Later still, Dr. Sivana organized a revamped Fearsome Five team comprised of Psimon, Jinx, Gizmo, Mammoth, and a newly-restored Shimmer. The team is a deadly combination as long as they can ignore their personal grudges for one another.
Major Story Arcs
For further details: Salvation Run
Psimon was among the second wave of villains sent to the prison planet by the Suicide Squad. He was savagely killed in issue two of Salvation Run by the Joker when he tried to convince the other villains that escape is impossible and they should try to build a new civilization. The Joker disagreed and proceeded to bash his head in with a rock.
Psimon appears as a member of the Brotherhood of Evil in episodes "Calling All Titans" and "Titans Together." He is part of small team to incapacitate Raven as the Brotherhood neutralize all the members of the Teen Titans. In the end, Psimon and the rest of the Brotherhood of Evil were defeated by the combined forces of all Titans.
Psimon appears in the Young Justice episode, "Bereft," voiced by Alan Tudyk. In the episode, Psimon is the cause behind the Young Justice members losing their memories of the past six months. He is in Bialya with a team of scientists to investigate an extraterrestrial sphere. After battling and being defeated by Miss Martian's telepathic abilities, he reports back to his employers, the mysterious group of The Light, who report the mission a success as they now have an operational way of delivering things.
He returns in Image, controlling the president of Qurac for Queen Bee. Again fighting Miss Martian, who he forces into her true white martian form and uses her fears to torture her, until she manages to again defeat him, rendering him in a catonic state.