Onimar Synn is a fictional extraterrestrial demon, a comic book character published by DC Comics. He first appeared in JSA #23 (June 2001), and was created by David S. Goyer, Geoff Johns and Stephen Sadowski.
According to legend, Thanagar was plagued by seven devil at the dawn of its history. None was more feared than Onimar Synn. Eventually he was defeated by the legendary hero Kalmoran and imprisoned in a vault of Nth Metal where he would remain for millennia. Countless years later, Thanagar grows powerful during his imprisonment, but is eventually devastated in a war with the Tormocks. During the rebuilding, Synn emerges and slaughters the ruling high council. He then sets about taking over the planet by gaining control over as much Nth Metal as possible. Through the metal's psychoreactive properties, Synn gains control over not just a unique metal, but the planet's racial memories as well.
Synn is opposed by the Hierophant, rebels made up of native Thanagarians as well as races that Thanagar had conquered over time. Transporting Kendra Saunders to their planet, she brings Hawkman back from the dead. Armed with a Nth metal gauntlet, the "Claw of Horus," Hawkman and the JSA battle Synn's zombified soldiers. However, the heroes are quickly overwhelmed and captured. Eventually, the team breaks free and faces Onimar Synn in gigantic form. Pulling Nth metal from all around to add to his size, Synn is so large that even Atom Smasher struggles to match his height, his new control over the fundamental forces of the universe also allowing him to disable the rest of the Justice Society, such as using his command of electromagnetism to negate the Flash's frictionless aura that protects him from sustaining damage at top speed, or severing the bonds that hold Sand's atoms together. However, Hawkman and Hawkgirl are able to defeat him by coming together and acknowledging their love. Their souls are so strong that they can disrupt his Nth metal body through the Claw of Horus.
Onimar Synn returns during the Rann/Thanagar War. Aided by worshippers, he is able to reform himself and renews his plans of conquest. However, he is defeated by a coalition of heroes and split into seven parts, each transported to the center of a separate sun so that he might never reform again.
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