Omega is a villainous version of Bruce Wayne from the limited comic series Batman: Last Knight on Earth. After society fell apart due to the machinations of Lex Luthor, Bruce gave up his ethics as Batman and became the tyrannical ruler of a post-apocalyptic Earth.
One night in Gotham City, Batman discovers the body of a young boy in Crime Ally and learns that the victim was related to his parents murderer, Joe Chill. Batman went to confront Chill in his apartment about the child, stating DNA tests match him as the boy's father despite the fact no records showed he had a son. However, Joe just taunts Batman as he cooks on his stove and reveals that he knows about his secret identity. Running out of patience, Batman grabs Chill just as a fire begins to spread from the stove onto the walls and threatens him for answers. But Joe implies the child really was his son and the murder of Bruce's parents was not for the pearl necklace Martha Wayne wore.
Batman later meets with Commissioner Gordon to assist him with replacing a light inside the Bat Signal. Gordon knew something was troubling The Dark Knight about his latest case and convinces him to talk about it. He reluctantly informs Gordon that the body found in Crime Ally was the son of Joe Chill who was estranged from his father at birth. However, all records about his existence had been confiscated by authorities after he died at Gotham presbyterian during a botched surgery performed on him by an inebriated Thomas Wayne. After the Waynes were murdered in Crime Ally, their estate payed to cover up the boy's death and make it seem what Joe Chill did to them was not out of revenge. All this information caused Bruce to question his motivations as Batman.
However, unbeknownst to the Dark Knight, Joker was actually the one responsible for his recent case. The Clown Prince of Crime cloned the boy throught to be Joe Chill's son using the crook's DNA and then planted fake documents which were aged by Chronos to make seem the Wayne family were hiding incriminating details about their past. Joker did this believing it would strengthen Batman's resolve for what he knew was coming in the near future.
Around this time, Lex Luthor decided to put an end to his feud with Superman once and for all by forcing the Man of Steel into a one-on-one public debate about good verses evil, with the loser to be impaled by Kryptonian shards buried beneath the ground. After both men made their speeches, they knew Superman was victorious between them. But as the shards sprang up under Luthor, Superman saved him at the cost of his own life. Now that the world's greatest protector was gone, people began to reflect on Lex's speech and soon turned on all forms of authority, including superheroes.
Those at the Hall of Justice tried to barricade themselves inside the building from the invading hoards. However Batman, being among the heroes there, decided to hold the door open and allow the hoards inside, as he had faith that they would not harm them. Unfortunately, the people proceed to tear Batman apart upon entering the building, which left him severely broken physically and mentally. Although many believed Bruce did not survive the attack, he somehow managed to recover from his various injuries without the need of magic or a Lazarus Pit and grew to resent the world for what had happened to him. He abandoned the mantle of Batman and instead forged the identity of Omega by rising above the angry mobs to acquire control of the Anti-Life Equation through the severed head of Darkseid and use it to enslave much of the worlds population from Wayne Tower for many years, quelling hate and anger at the cost of free will. However, Bruce's old ally Tim Drake found a way to block the signal emitting the equation, freeing the Bat Family and a hundred more people from Omega's control.
Bruce eventually found a more efficient way to spread the Anti-Life Equation across the planet by using the telekinetic powers of Martian Manhunter, who was brainwashed into serving Omega. But before commencing his plan to amplify the equations effects, Omega decided it was time to create a successor to rule in his place. He had his old butler Alfred Pennyworth make a clone of Bruce Wayne in his prime so it could be conditioned to become the next Omega. But Alfred had his own plans for the clone, and upon its creation, he flees with young Bruce away from Gotham in hopes he can convince him to live a life free of Batman and in safety from Omega's forces. Unfortunately, Omega manages to track Alfred down and has Scarecrow (one of many villains now under his control) inject a lethal chemical into his body which slowly claims his life. As Alfred dies, Omega makes him believe that he stopped the Waynes from going to the theatre on the night of their murder, giving Alfred a peaceful demise.
Meanwhile, Omega's young clone has taken the mantle of Batman to end Omega's reign with help of Wonder Woman, the surviving members of the Bat Family, and the Joker, who is now a living disembodied head in a jar. After making their way back to Gotham, Batman and Joker infiltrate Wayne Tower in search for Omega while their allies attempt to stop Martian Manhunter from spreading the Anti-Life Equation worldwide. However Omega had already anticipated the groups assault and used it to ambush his opposition and capture Batman. Omega restraints his clone to the Mobius Chair, which was modified to brainwash Batman into becoming his successor. He then removes his mask after realising Batman did not know his true identity and was accused of being an abomination rather than a savior like the original Dark Knight.
Omega claimed that he was saving the world by keeping everyone under his control, so that the chaos and anarchy started by Lex Luthor would finally end. He hoped young Bruce would have seen things his way after venturing through the unforgiving post-apocalyptic wasteland that humanity's various wars had created since Lex's speech. Regardless, Omega was confident the Mobius Chair would make Batman take his place and then left for Wayne Manor, which was now located on top of Wayne Tower.
Batman soon manages to escape his predicament and follows Omega to the manor for a final showdown. Omega uses the spike Darkseid's head was hung on to impale Batman through his torso after claiming what he was doing was the only way to save everyone as they no longer looked up to heroes and that they would destroy each other without guidance. However Batman takes the spike and smacks Omega with it before jamming it through his throat, killing him and ending his reign.