In the world of comics, a character's "unintentional" death or severe injury is rarely seen, partly because it doesn't make sense to kill off or hurt the title character of a series and partly because death is used as a last resort reboot option when sales start to drop. Naturally, our favorite heroes and villains have developed fun traits such as regenerative healing or straight-up invulnerability to most things that might come their way, save one or two special weaknesses.
Check out this list of the toughest superheroes and strongest comic book villains and see who really is the best of the best!
With powers originating from Wolverine's genetic mutation, Wade Wilson, a.k.a. Deadpool, is a product of the Weapon X program and as a result, has Wolverine's healing abilities. At one point in the comics, Deadpool becomes infatuated with Death (note the capital 'D'), the same Death that Thanos is in love with. Thanos then "gifts" Mr. Wilson with immortality, preventing him from ever being able to fully "be with" Death.
Between the healing factor and his immortality, Deadpool has never and will never truly die in the comics (and hopefully the films, providing Fox and Marvel Studios get their stuff together and collaborate on something amazing).
Logan's initial mutation is a healing factor that allows his body to regenerate over time. Coupled with his adamantium skeleton, Wolverine is, for the most part, unkillable as long as a portion of his biological self remains to regenerate after combat - with a few notable exceptions. Kitty Pryde succeeded in killing him in a What If? one-shot by phasing her hand through Logan's skull and into his brain, losing the hand in the process.
The primary weakness with healing factor powers is centered around the amount of time required for them to work. If someone were to attack Wolverine at a rate faster than he'd be able to heal, then Wolverine really isn't that big of a threat. Further, in the 2014 Death of Wolverine run, Logan's healing factor is effectively worn out and he begins to experience rapid aging while people try to take him out.
The Hulk is an interesting nut to crack - literally. In addition to having arguably the highest degree of physical strength in the Marvel Universe, Bruce Banner's Hulk is also known for his impervious skin, heightened agility, resistance to gamma radiation, a regenerative healing factor, and most importantly, a superhuman level of inelegance.
Presently, Bruce Banner's Hulk is dead. In the recent Civil War II run, Bruce is visited by a group of heroes concerned with a vision the Inhuman Ulysses Cain has, which involves Banner transforming into the Hulk and going on a rampage, killing several heroes. Hulk's death is at the hands of Hawkeye, who was given a special arrow by Banner himself in the event Banner was ever going to transform into the Hulk again, which, when confronted by a legion of super heroes that are supposed to be your allies, is bound to happen.
Doctor Manhattan is basically God with a massive blue penis. Born Dr. Jonathan Osterman, Doctor Manhattan has technically only died once, and that was during the accident that turned him into the being he is today. Without exaggeration, Doctor Manhattan's powers are nigh limitless including, but not limited to: time vision, precognition, immortality, super strength, telekinesis, reality warping abilities, a bevy of abilities centered around limitless nuclear energy, molecular reconstruction, in addition to his previously existing genius-level intelligence.
As it's seen in Watchmen, Manhattan's main weakness comes from within himself. Because of his predicament of omnipotence, he's slowly become less "human" over time, making those moments of human emotion he experiences at points more jarring, until the climax of the novel.