The amount of superheroes who have died at some point in their comic book career is shockingly high. However, the number of supervillains who have killed superheroes is comparatively low. Heroes die though all sorts of different means. They're often the subject of a heroic sacrifice, and they routinely kill each other. Seriously, superheroes kill people all the time.
But incidents where superheroes are killed by their villains are actually pretty rare. One might think this would be the most obvious way for a costumed crime-fighter to go out, but it seems either supervillains are incompetent, or comic book writers can’t find many ways to make getting murdered look heroic.
The pages of Marvel Comics are rife with amazing and deadly villains. Bad guys like Loki, Doctor Doom, the Red Skull, and Kingpin all have intimidating reputations (and rightfully so), but that doesn’t mean they’ve managed to actually kill their rival heroes. In the Marvel universe, antagonists often seem to come up just short of gaining their ultimate vengeance. However, every so often, a supervillain gets lucky and actually manages to cut down a superhero. It’s so rare, it's a tragic surprise each time it happens.