The comic book medium has always killed characters for the sake of drama, only to bring them back after a period of time. The big two companies, Marvel and DC, have been equally guilty of this with notable resurrections like Superman and Jean Grey. These resurrections are usually done due to fan demand or to restore the status quo which helps new readers.
But sometimes, there are rare cases when comic book characters actually stay dead. So, why does this happen? One reason is that the hero or villain themself was not popular to begin with, so killing them was the only logical course of action. Another reason is that these characters' deaths were so impactful that bringing them back to life would cheapen their demise.
Now, keep in mind that the ones that will be mentioned here are those who stayed dead and have not properly returned to their respective comics. Also, origin story figures like Superman's parents or the Waynes will be limited, as the entire list could consist of characters like them. Finally, as these will be dealing with major deaths, there will be spoilers ahead.
The powers of Thor have been passed down to several characters throughout the years, and one notable individual to receive this honor is Eric Masterson. Though he'd start off as the God of Thunder's alter-ego, Eric would eventually gain his own mantle and weapon as Thunderstrike.
In his own comic book series, Masterson would confront numerous foes but none of them would be as dangerous as Bloodaxe. This villain was Jacki Lukus, who received powers upon using the axe used by Skurge the Executioner. But while our hero would eventually separate the woman from the weapon, he consequently managed to gain the power of both Thunderstrike and Bloodaxe, which became a problem.
Thunderstrike would confront the deadly weapon in his own subconscious as Bloodaxe would take the guise of its owner, Skurge. Though Eric would eventually defeat the axe, the aftermath results not only in the destruction of the weapon but Thunderstrike and Eric himself.
Despite staying dead since the '90s, Eric Masterson's legacy lives through his son, Kevin, who has taken the mantle of Thunderstrike and continues to embody the everyman superhero.