In one Marvel Comics world, the children of the Fantastic Four and the X-Men would together create one of the world's strongest and most dangerous mutants. The reality-hopping Exiles team found themselves on a world where most of the world's superhumans were either dead or in captivity, with David Richards responsible for it. This son of Franklin Richards and Rachel Summers was believed to either grow up and save his world from the Sentinels that killed his parents, or grow up to become its new tyrant. Despite the Exiles' good intentions, they learn that some destinies are inevitable, as David's path appeared to be destined for darkness no matter what.
In Exiles #12 by Judd Winick and Mike McKone, the Exiles meet another team called Weapon X, a group of individuals from other realities who are comfortable with lethal solutions to their missions. They learn that this world has been overtaken by the Sentinels who keep the surviving superhumans in captivity with inhibitor collars on to neutralize their powers. Both teams together storm a base where they rescue a group of mutant children, including their target, David Richards. They learn that David's mutant powers will be strong enough to defeat the Sentinels, but instead of granting freedom, he'll seek to enslave humanity's survivors. While Weapon X and the Exiles argue and fight over the orders to kill him to prevent this future, the Exiles agree that former Weapon X leader Sabretooth will stay behind to raise David and the other children, hoping his influence will prevent the future they were foretold.
In Exiles #59 by Tony Bedard and Mizuki Sakakibara, it is revealed long-time Exile Blink returned to that world to find David and the other children all grown up, Sabretooth's protection and lessons keeping them alive long enough for their mutant abilities to manifest after puberty. Taking especially good care of David, Creed became just as proud of the leader and fighter he became as he did raising Blink during the Age of Apocalypse. After mentally probing Blink's mind to assure she wasn't a spy, she witnessed the full might of David's power during their final battle against the Sentinels, described as "if you rolled Professor X, Magneto and the Phoenix Force into one, you'd begin to approach what this kid was capable of."
Franklin Richards' powers to rewrite and control reality combined with Rachel Summers' Phoenix Force means David would grow up to become an Omega-level mutant, able to easily protect or destroy the remainders of humanity on his world with little effort. Aware of the future that could be, the Exiles hoped Sabretooth's guidance and presence could make a difference at preventing this outcome. Despite Victor's good intentions, David began to show signs that some paths are inexorable as he began to use his powers maliciously. He used his abilities to pry into Blink's mind without her permission and after they defeat the Sentinels, he took control of her mind and powers to teleport to a secret location where he had hidden people responsible for the Sentinels and camps. He forced Blink to use her powers to torture and kill those people, seeking revenge for the wretchedness he and others suffered with a remorselessness and glee that screams "supervillain" and not "superhero."
This macabre suffering ended when Sabretooth, having found their location, used an old inhibitor collar to mask his approach where he killed David by ripping his heart out. Despite the trauma which remained with Sabretooth and Blink in future Exiles missions, David's powers supposedly allowed him to return to life, proving this combination of the X-Men and Fantastic Four's greatest powers is absolutely horrifying.