He was portrayed by Stink Fisher.
Aaron Helzinger was imprisoned at Arkham Asylum after killing his family with his bare hands.
As an inmate at the asylum, Aaron ended up being seduced by Barbara Kean who requested that she "protects" him when Jerome Valeska convinced her to try and befriend Richard Sionis. When a new prisoner, the self proclaimed "Zaardon", arrived, he collapsed and a blue gas escaped from his mouth, knocking out Aaron and his fellow inmates. They are captured and taken a penthouse, and given the opportunity to work for Theo Galavan to cause chaos in Gotham in a team named the Maniax. Everyone but Richard Sionis (who was killed) agreed to be part of the group.
Aaron and his fellow escaped convicts threw several men from a rooftop, with each letter sprayed on them spelling out MANIAX! and spreading their message.
During their attack in the Gotham City Police Department, Barbara lured out her ex-boyfriend James Gordon and he ended up being beaten and attacked by Aaron. The pair of them then made their escape, leaving Gordon to stagger back and discover the massacre the Maniax carried out.
Helzinger is eventually recaptured and brought back to Arkham Asylum. There he meets Oswald Cobblepot, who due to a test of Professor Strange is the only inmate with ice cream on his food tray. Impulsive, Aaron Helzinger sits in front of Oswald and sees the ice cream. Oswald is willing to give Aaron some, but Helzinger violently grabs Oswald and beats him, but Oswald remains docile. Seing that his test is successful, Strange sends the security to restrain Helzinger.
To find out if Cobblepot's treatment was a success, Strange decides to put Oswald to one final test . Strange arranges for Oswald to be put back in the treatment room, but he sees he's not the only one there. Oswald finds Aaron strapped to the treatment chair, blindfolded and a table with a knife and water. Oswald picks up the knife first while Stragne and Ms. Peabody watching from a hidden room, but let him proceed. Oswald removes the blindfold from Aaron and instead of killing him for revenge, he uses the knife to cut his straps and hands him the glass of water, thereby passing the test.
A few weeks later, Helzinger attacks another inmate for calling him fat. Edward Nygma steps between the two and deescalates the situation. Helzinger even apologizes afterwards.
Later, Strange has Aaron Helzinger brought into Theo Galavan's cell and provides Theo with a case containing the 'Sword of Sin'. He tells Theo that Helzinger is a demon and that the case contains everything Theo needs to destroy him. Despite Strange's expectations, Theo simply uses the case to knock out Helzinger instead of killing him with the sword.