Frank Castle, aka The Punisher, is one of Marvel's most lethal figures, an anti-hero with no constraints about murdering the criminals he encounters over the years. As a result of how difficult his personal war on crime can be, it only makes sense that the Punisher has been killed on more than one occasion only to be restored after each time.
Here's every major time the Punisher has been killed over the years and how he was restored.
SUICIDE RUN
The twelve-part Suicide Run" -- which crossed over into The Punisher, The Punisher: War Journal, and The Punisher: War Zone -- focused on a meeting of powerful crime families at Manhattan Tower, designed as a trap for Punisher. Aware of the danger but convinced that the chance to kill so many criminal bosses was worth the risk, Frank Castle snuck into the building through the garage, leaving a truck full of explosives behind him. Confronting the crooks, Punisher detonated the explosives, killing all the criminals and seemingly himself in the process, with the FBI falsely claiming to have discovered his body in the wreckage.
In reality, Castle managed to survive the explosion and recuperated with an innocent young woman in the small town of Laastekist. Meanwhile, Outlaw -- a British anti-hero inspired by the Punisher to follow in his footsteps -- traveled to America to investigate. He came up against a number of copycat Punishers who rose up following his demise and eventually worked alongside the Punisher's primary allies to fight back against the coalition of enemies who eventually learned the truth and tried to kill Castle in Laastekist.
ANGEL PUNISHER
The fifth volume of Punisher, by Christopher Golden, Tom Sniegoski, and Bernie Weightson, opened with Frank Castle having been manipulated into killing himself by a horde of demons -- including ones with ties to the criminals who had killed his family and set him on the path of vengeance in the first place. Restored to the world of the living by the angel Gabriel, Punisher was given supernatural powers as he continued his war as an agent of heaven -- this time focusing on the demons who'd been manipulating his whole life.
By the time of "Welcome Back, Frank" by Garth Ennis and Steve Dillon, Punisher had been restored to flesh and blood. The Punisher seemingly off-panel grew exhausted with the missions heaven sent him on, and he was eventually sent back to his former life as a form of punishment. The Punisher casually accepted his return, almost immediately retuning to his previous way of doing things.
DARK REIGN
During the events of Dark Reign, Norman Osborn wrestled control of many facets of the Marvel Universe away from the heroes. He then set about completing a list of missions, each of them meant to help shore up his power base. One of these missions was to kill Frank Castle. In Dark Reign: The List -- Punisher by Rick Remender and John Romita Jr, he ordered Daken to lead a squad of soldiers to kill Castle. After an extended battle, Daken was able to wear down the Punisher and decapitate him, seemingly killing the vigilante once and for all.
However, the remnants of Castle were discovered by Man-Thing and the Moloids, who brought him to Morbius in the underground Monster Metropolis. Castle was reborn as Franken-Castle, a patchwork man designed to help defend the monster community from attacks. He got his rematch against Daken and fought alongside the Legion of Monsters before Elsa Bloodstone gave him the Bloodstone, which restored him to his original form.
THE MULTIVERSE
Across the Marvel Multiverse, there have been plenty of versions of Frank Castle -- with many of them dying inglorious deaths due to their relative wars on crime. Punisher: The End by Garth Ennis and Richard Corben saw Punisher, one of the last survivors of a nuclear war, kill a room of powerful government officials (and potentially doom humanity) before walking into the radioactive fires ravaging the ruins of New York. In Punisher Kills The Marvel Universe by Ennis and Doug Braithwaite, Castle wipes out most of the hero and villain community before turning his gun on himself.
Punisher: MAX by Jason Aaron and Steve Dillon ended with a fatally wounded Castle dying while trying to return to the home he once shared with his family, inspiring a legion of copycat Punishers in his wake. After accidentally killing a family of innocents in Earth X #1/2 by Alex Ross, Jim Krueger, and Bill Reinhold, Punisher committed suicide. There have also been numerous What If? stories in which the Punisher meets his end, notably including during his brief stint as a vampire hunter in What If? Wolverine Was Lord of the Vampires by Roy Thomas and Tom Morgan.