In a bid toward manufacturing immortality, an alien race used the harsh surface of prehistoric Krypton to produce a subject that would be killed repeatedly but then cloned following its demise. Over a span of decades, the subject underwent accelerated evolution becoming virtually unkillable (able to eventually regenerate itself from death with newborn immunities) but whose treatment made it a killing machine. Murdering those that created it, the subject would become known as the Ultimate and would travel from world to world wiping out all life it found for hundreds of thousands of years. Eventually, the Ultimate would find its way to Earth where it became known as Doomsday. Therein, Doomsday was drawn to Superman whose Kryptonian DNA descended from the species that created and tortured the creature. When the combined efforts of the Justice League failed to stop Doomsday, Superman and the monster fought until they beat each other to death. While Superman would later be regenerated with the help of Kryptonian technology, Doomsday itself would regenerate thanks to its abilities. Doomsday would subsequently return repeatedly as a reoccurring threat for the Man of Steel. Following Flashpoint, Doomsday became a creature that attacked Krypton only to be imprisoned in the Phantom Zone and employed later against Superman by Brainiac. Superman would be forced to kill Doomsday only to be infected by the creature, essentially merging the two. The Man of Steel would turn that newfound power against Brainiac and drive the infection out of his system. A new, smarter Doomsday would emerge following DC Rebirth. In the series Young Justice, the character Match shared a number of characteristics with the likes of Match, Bizarro, and Superboy-Prime from the comics and in his last appearance, he started to resemble Doomsday.
Prior to the Crisis on Infinite Earths, Rick Flag was a pilot and leader of Task Force X (better known as the “Suicide Squad” over the degree of danger in their missions) whose son carried on his name and followed in his footsteps. Following the Crisis, both Rick Flags were essentially merged as the Suicide Squad evolved from a team of soldiers and scientists into a group of supervillains commuting their sentence for service under the direction of Amanda Waller. Featuring rogues like Deadshot, Count Vertigo, and Captain Boomerang (and even heroes like Nightshade, Nemesis, Bronze Tiger, and Roy Harper), the Suicide Squad walked a fine line between heroes and villains. While used as a tool for the sake of the United States, they generally undertook missions that could be described as unsavory. Batman would unsuccessfully try to dismantle the Squad only to be stopped by Waller who threatened to expose the hero’s secret identity. Eventually, the Justice League would come to blows with the Squad (as Flag and Batman fought to a standstill) that would lead to Batman quitting the League. Eventually, it would be believed Flag was killed on a mission against the Squad’s nemesis the Jihad. The Squad would persist for years, becoming a powerful tool for President Lex Luthor before being disbanded and more-or-less living on in spirit in a group of mercenaries called the Secret Six. Eventually, it would be learned Flag was alive and a prisoner of the nation Qurac. Bronze Tiger would save him and Flag would subsequently rejoin the Squad. Following the events of Infinite Crisis, it was revealed Rick Flag was actually a soldier named Anthony Miller brainwashed by General Wade Eiling into believing he was the son of war hero Rick Flag. Flag would essentially vanish with the events following Flashpoint (largely replaced by Deadshot) only to emerge following DC Rebirth as the Squad’s leader again. Belle Reve Penitentiary, generally considered the headquarters to the Suicide Squad, featured prominently in the series Young Justice.
The death of Iris West Allen sent the Flash on a downward spiral. The hero would inevitably go on to give his life in the event Crisis on Infinite Earths. However, it would be revealed Iris did not in fact die and instead returned to her native time period of the 30th century. Prior to his death, Barry Allen would join his wife in the future and the couple would raise their children Don and Dawn together for a brief period. In their time, metahumans are feared and superheroes are outlaws. Inspired by their mom’s stories of their father, Don and Dawn decided to become the heroic Tornado Twins and fight for justice. Don would go on to have a son in Bart Allen who would go back in time to become the hero Impulse and learn from his adopted cousin Wally West (who replaced Barry as the Flash). Bart’s mother Meloni Thawne would also have another son with a time-displaced Captain Boomerang in Owen Mercer (who adopted his father’s mantle). Dawn would go on to have a daughter in Jenni Ognats who became the hero Xs and member of the Legion of Super-Heroes. Wally would go on to have children in Jai and Iris with his wife Linda Park-West that he would refer to as the Tornado Twins (Iris would adopt the mantle of Impulse from Bart). The West family was heavily altered following the events of Flashpoint so its unknown how much of Iris’ past existence remains. Bart Allen would become instead Bar Torr who has a completely different origin. Xs would not emerge. Don and Dawn Allen are briefly mentioned in the second season of Young Justice when Impulse reveals his grandmother is pregnant with his father and aunt.