Deegan was born and raised in Gotham City. He graduated with a PhD and an MD in psychometrics, and became a psychiatrist at Arkham Asylum. His methods were bordering on torture conflated with illegal experimentation, however, he was never convicted and avoided prison over the years; due to technicalities. Despite this, Deegan did not get off completely scot-free; in 2013, his medical license was revoked and he was fired from the medical board.
The mad scientist
One evening, Deegan was giving a presentation on his patients and how they could become Meta-humans with the help of eugenic insights, but his audience then perceived him as insane and left before he even started elaborating, much to his disappointment and frustration. As he walked in the parking lot, he was approached by the Monitor, who Deegan thought was a prankster trying to get some laughs, before Novu smashed his car in order to demonstrate his power and get his attention. When Deegan asked what the individual was, he remarked that he was something beyond his comprehension. The Monitor then gave Deegan the Book of Destiny, granting him the power to manipulate reality as he sees fit.
He tried to reshape reality with the intention to become The Flash, but miscalculated and caused Oliver Queen and Barry Allen to swap powers and identities.
Meeting the heroes
When Oliver showed up at Deegan's office in Arkham, he recognized and told him that he understood why he didn't become the Flash, stating that changing reality must have a "learning curve". As Oliver ordered him to fix reality, Deegan answered that he doesn't want to and runs away after releasing Arkham's inmates. When he retrieved the book from its hiding spot and was about to rewrite reality,[Kara Danvers appeared and took the book from him, to which he quickly escaped.
Later, the Monitor appeared to Deegan once more in his lab holding the Book and asking him to think bigger. Deegan rewrote reality, on a larger scale.
A brave new Elseworlds
After rewriting reality again, Deegan kept the book in the Time Vault, dubbed the "Fortress of Solitude"]], jumbled everyone's lives, turned Oliver and Barry into criminals known as Trigger Twins, and took on the form of Clark Kent, whose only record on Earth-1 was with his fight with A.M.A.Z.O.. He then pursued the Trigger Twins but was distracted when they caused an accident where he had no other choice but to protect the civilians and let them escape. Later at S.T.A.R. Labs, where he redesigned it as his headquarters, he ordered his agents John Diggle and Caitlin Snow to find them.
He proceeded to the S.T.A.R. Labs particle accelerator and conversed with "Subject One", Kara Danvers, who he locked up and drained off of her powers for himself, leaving Kara with a weaker version of her abilities. He revealed to her how he got the idea of his appearance and powers. Kara, in rage of Deegan's desecration of her family crest and her cousin, tried to break the glass, before Deegan's agent, Alex Danvers, administered a high-pitched sound to throw her off-balance, to which Deegan stated that the cells are patrolled 24/7. When agent Danvers left, Kara tried to call out to her, and much to Deegan's amusement, he threatened his own agent's life if Kara got any bright ideas of escaping, to which Kara called her a monster. Deegan said he was otherwise Superman.
Later, he caught Alex Danvers breaking out Kara Danvers and was about to kill them when Barry, Oliver, Cisco and Clark breached inside S.T.A.R. Labs just in time for Clark to distract him. The two supermen battled within Central City, and civilians perceived them as Superman fighting one of his enemies, Bizarro. Deegan overpowered Clark and was about to finish him off, when Kara used her heat vision to throw Deegan into the air, and gave the Book of Destiny to Clark, restoring Barry's, Oliver's, and Kara's powers and abilities. Deegan saw this and threatened to snap Barry's neck if Clark didn't close the book. Oliver countered this by threatening to shoot a Kryptonite arrow, but let Barry talk him down to do otherwise. Deegan then saw an opening to create a thunderclap and escaped with the book.
Deegan tried to restore his Elseworlds in the middle of a crowded street, where police officers tried to stop him from causing mayhem, but were turned into helpless taxi drivers. He then summoned A.M.A.Z.O. from the Book of Destiny and kept Superman at bay, when J'onn J'onzz, Lois Lane, and Querl Dox breached in to assist, before A.M.A.Z.O. locked in battle with Brainy. Lois used the Solar hammer from the Fortress of Solitude and kept Deegan off-balance, but not long enough for Clark to take hold of the book. Deegan retrieved the book and aimed it's energy at Clark and then at Lois, sending her flying. Barry and Kara successfully slowed down time, which gave Oliver the chance to shoot the book with a powerful arrow of metaphysical nature, overloading it with energy and destroying it's powers, and reverting reality back to it's original state. The accumulation of energy also disfigured Deegan's face and cognitive abilities.
Inmate at Arkham
John was then locked up at Arkham Asylum, this time as a patient, where he became friends with Roger Hayden, who told him not to worry as, due to his to actions, "the stage was set" and soon "worlds will live, worlds will die, and the universe will never be the same".