Kesselring

"We understand your anger, Mr. Castle. We have felt the impotent fury at the supermen who destroyed our lives, who forgot about the pain they caused, and hid behind their masks and capes and badges. But you: you dared to hit back. We want them all. The heroes and the villains. The mutants and the monsters. Anything that calls itself a superhuman: we want you to kill them all."

- Kesselring giving his offer to the Punisher

Kesselring is the main antagonist of Garth Ennis' 1995 Punisher Kills the Marvel Universe comic book one-shot. An American millionaire with a personal vendetta against superhumans, Kesselring sees an opportunity to wipe them out from the face of Earth when Frank Castle gets sentenced to life imprisonment after killing some of the heroes who accidentally caused the deaths of his wife and children, leading Castle to become the Punisher under Kesselring's service.

Past
According to Kesselring, he once was a normal American millionaire who enjoyed a luxury lifestyle on the high society. However, it all changed when he got inadvertently involved in a superhero fight. During the fight, Doctor Doom threw the Human Torch against Kesselring, horribly burning and scarring him for life and possibly rendering him blind from his right eye, leading him to wear an eyepatch. The Human Torch later apologized, but Kesselring didn't believe his apology to seem entirely sincere.

After his accident, society turned their backs on him and Kesselring swore to destroy all superhumans on Earth. From then on, Kesselring gathered other people who were inadvertently harmed by superhumans and together tried to devise a way to get rid of superheroes, supervillains, mutants and monsters.

Punisher Kills the Marvel Universe
After Frank Castle gets sentenced to life imprisonment for the murders of Cyclops, Hawkeye and Shadowcat when trying to avenge his family, who had been accidentally killed during a fight between the Avengers, the X-Men and the Brood on Central Park, Kesselring managed to get him bailed out during his transfer by paying the guards and falsifying his arrival on Ryker's Island. Once Castle arrived to Kesselring's manor on the Adirondack Mountains, Kesselring introduced himself and gave him a tour through his house before bringing him a room full of his associates, telling Castle how he and his associates suffered many tragedies thanks to superheroes, whose apologies did not seem entirely sincere. Accepting Kesselring's offer, Castle asked him for the necessary equipment and resources to start the job, becoming the Punisher.

In his first three days under Kesselring's orders, the Punisher managed to kill Spider-Man, Venom, Hulk and the Kingpin, but the latter's corpse got Castle stuck until the New York City Police Department arrived and took him into custody to be sentenced for life imprisonment like previously. However, Kesselring bailed out Castle again yet warned him to avoid being arrested as its cost was high. Using the Kingpin's equipment, the Punisher tracked down Doctor Doom to Latveria and killed him, avenging Kesselring's injuries to then rob a nuclear warhead from Doom and nuke the moon to wipe out the X-Men and the Brotherhood of Evil Mutants, led by Storm and Magneto.

In the next five years, the Punisher continues his superhuman-hunting crusade and succeeds in getting rid of many other heroes, including the Fantastic Four and most of the Avengers. After killing Wolverine, the Punisher gets arrested yet Kesselring bails him out once again to allow the Punisher to track down and kill Captain America. Upon returning to Kesselring's manor, while Kesselring tries to toast for him and his crusade, the Punisher makes clear his intentions to cease contact with him once Daredevil, the last superhuman alive, is eliminated, as what he does isn't for a celebration. Still desiring the superhumans to go extinct, however, Kesselring informs Castle that once Daredevil is dead, a new generation of heroes will inevitably arise to oppose them, so his crusade will never be complete. Neverthless, Castle refuses to kill innocent superhumans, including children, who have did no harm to anyone as of yet. Enraged due Castle's decision, Kesselring draws a gun and points him out, assuring him that he needs to halt at all costs that new generation because he's his "murder machine". Having enough and realizing that Kesselring has let his pain to consume himself, the Punisher swiftly draws his gun and shoots Kesselring to death, warning his associates to not mess up with him again or otherwise they will suffer Kesselring's fate.

Despite his death at the hands of the same man who aided on his schemes to exterminate superhumans, Kesselring's desire to see all current superhumans dead became fulfilled when the Punisher killed Daredevil, only to then kill himself upon realizing that he became what he swore to destroy. However, as a consequence of Castle's and Kesselring's actions, the Earth will have to wait a long time for a new generation of heroes to arise.

Trivia

 * In spite of his sole appearance, Kesselring is, so far, one of the most dangerous and cataclysmic villains from Marvel Comics, as his actions led to all superhumans, either heroes or villains, to be killed in an attempt to make them extinct, which in turn has left his Earth defenseless from extraterrestrial or interdimensional threats, like Galactus or Thanos, as there will be no heroes to oppose them, essentially dooming his world.
 * Alternatively, however, it's possible that the Punisher didn't kill heroes who weren't on Earth during the five years of the Kesselring's campaign against superhumans, as he was never depicted leaving Earth for the outer space. If those heroes were thus spared from the Punisher, maybe there's still a chance for Earth-95126 to survive great menaces.
 * Despite the fact that the Punisher later kills him and is the titular protagonist of the one-shot, Kesselring served as The Heavy because his offer to give the Punisher all necessary equipment to get rid of the world's superhumans drove the plot of the story, which made the Punisher the Big Bad and the one behind the plot.