On the comic book page, live-action movies, or even cartoon TV shows, Wolverine has proven to be one of the most ruthless and efficient killers in the Marvel Universe. Honestly, it would be hard to even know how many lives Logan has ended with his razor sharp claws alone. But not every kill Wolverine makes is a righteous one.
In "Ultimate X-Men #41," a young boy learns that developing a mutant power isn't always a dream come true. Instead of a superpower, he gets a curse, causing every person, family member, friend, and even dog around him to burst into flames, and burn to ash. It isn't long until Wolverine tracks him down. Cracking a beer, Logan tells him there's no cure his mutation, and even worse, nobody can ever find out that a mutant could kill over 200 people by accident, or they wouldn't even trust the X-Men. Since the boy can't go on living, there's only one thing to do. Readers only get to see Wolverine exit the cave, but it's obvious he put the innocent boy down before he could kill again. It might be the so-called hero's most haunting kill, and more than any other, raises questions about what being a hero really means when lives are on the line.
It seems like even the funniest superheroes get their darker stories, and for Spider-Man, it came in the form of "Reign," a limited miniseries taking plenty of influences from Frank Miller's "Dark Knight Returns." Set in an alternate future when Peter Parker is close to 70, and long retired from the job, the former webslinger returns to the streets when crime gets out of hand. But it's the death of Mary Jane Watson that keeps him up at night.
It's bad enough that Peter leaves Mary Jane dying in a hospital to foil a crime, but as the story goes on, readers learned that Peter was responsible for her death... in the worst way possible. You see, the doctors can't figure out why MJ is dying of radiation poisoning, but Peter can... since his blood - and ALL his bodily fluids - are radioactive. That's right, in the darkest, creepiest, most unsettling Spider-Man story we know of, Peter Parker's decision not to use protection killed his wife.
Still not shocked or convinced this was Peter Parker's worst murder, no matter what the future holds? Look no further than him comparing her illness to spider eggs hatching inside of her, spreading cancer throughout her body.
Man of Steel took plenty of heat for showing Superman killing his enemy, but ask a die-hard DC fan, and they'll tell you that "Superman doesn't kill" isn't exactly true, since more than a few people and enemies have fallen at his hands. But no kill is stranger, or harder to believe, than the one taking place on an alternate world the Man of Steel accidentally stumbled upon.
On this parallel Earth, three Kryptonians sentenced to the Phantom Zone escaped their prison to wreak havoc on Earth - and they did. By wiping out the atmosphere, the villains, General Zod among them - managed to kill 5 BILLION souls in a matter of minutes. In a strange departure from his usual character, Superman immediately decides that he has no choice but to act as judge, jury, and executioner. Sentencing the three to excruciating death, exposing them to green kryptonite.
We know what you're thinking: since he started his comic career as a soldier in World War 2, it's no fair to call Captain America a killer. While his wartime kills can mostly be written off, murdering people turned out to be a hard habit for Cap to kick, since he was getting in trouble for killing suspects in even modern times
But to see Cap's worst streaks of killing, look no further than Marvel's Cinematic Universe. Even if we pretend that smashing the edge of a metal shield made from Earth's toughest metal into someone's skull isn't enough to kill them - even without super strength - it doesn't explain Cap's desire to throw normal soldiers to their deaths from flying aircraft, riddle them with machine gun rounds, or just snap their alien necks.