Aaron Helzinger was a man who suffered from homicidal rage and was institutionalized in Arkham. When threapy and drugs could not help him they began using experimental surgeries, most notably the removal of his amygdala, the section of his brain that processes emotions and memories.
The surgery however only caused him to have even less control over his rage and gave him superstrength. Though generally peaceful, Amygdala can easily be manipulated do to his relatively mindless state, making him a tool for other Batman villains.
When Jeremiah Arkham went insane, he unleashed Amygdala on Batman , though Batman managed to defeat him. Amygdala would reappear when Bane broke all the inmates out of Arkham and soon fell under the sway of the Ventriloquist & Scarface. When Batman tried to stop them a fight with Amygdala errupted, allowing the Ventriloquist & Scarface to escape.
Amygdala was eventually befriended by Nightwing and became the warden at Lockhaven Prison. Amygdala even became Nightwing's roommate. Unfortunately, a villain named Blockbuster blew up the apartment building. Amygdala and Nightwing survived, but Amygdala went out of control with rage and had to be subdued. Becoming a villain once again, Amygdala joined the Secret Society of Super Villains.
- He later appears in the episode Justice League Unlimited in the episode "The Cat and the Canary" as a member of Roulette's Meta Brawl.
- He appears in Season 2 of Gotham as one of the seven members of The Maniax named Aaron Helzinger.