Look, I apologize in advance: I wrote this thing a while ago and it's huge, and I have no way to make it smaller.
The Superhero Comic Book was born, more or less, in the late 30's with the invention of Superman. (We can argue if Mandrake or The Phantom count as costumed super heroes some other time, okay?) Followed by Batman, the Green Lantern, the Flash, Captain America and a cavalcade of remarkably brightly colored men and women (like the Phantom Lady, who wore a remarkably skimpy costume decades before Ed Benes was a twinkle in Michael Turner's eye... wait, Ed Benes isn't Michael Turner's son? Oh. Well, neither of them was alive back then anyway.)
The superheroes inherited the moral code of their pulp forbears like Doc Savage, the Spider and the Shadow, as seen by Superman standing there grinning while people died to poison gas or Batman using an airplane machine gun to mow down mindless deformed giants. As such death was a relatively common, and relatively final, affair.
Major villains like Hugo Strange, the Ultra Humanite, the Joker or Lex Luthor were an exception, but the way this was dealt with was also befitting the pulps which were comics direct ancestors. Basically, You Never Saw The Body. Island headquarters would explode, mad clowns would fall off of cliffs like Moriarty in greasepaint, vats of chemicals would have strategically placed vents that led to fast moving rivers.
When a writer creates a suitable villain he or she is often loathe to lose such a useful tool, and so You Never Saw The Body. After a suitable amount of time had passed, the villain would return, cackle some about how the hero had thought that those dinosaur robots had killed him but no, and now the time was ripe for revenge, hahhahahahhahhahahhaha. It was all very ritualized.
Some characters, meanwhile, were created entirely so that they could die. Thomas and Martha Wayne were effectively 'born dead', so to speak. They exist only to be dead so that Batman has a better reason than an insane fetish for his actions. The entire populace of Krypton were born to die, (depending on if the writers have bottle cities in their particular version) to get blown up as a lesson in hubris.
Uncle Ben is dead, baby, and Peter Parker is not ever getting over that one because then he'd probably stop running around in a red and blue unitard and we'd have to call the comic "Peter Parker, the Unremarkable Regular Man". Even Howard Mackie didn't go that far and he cloned just about everyone else in the book.
However, neither of these categories includes when main protagonists die in comic books.
This is because at first, that didn't happen. How would it? Superman's not going to die in his own comic book. This constraint bothered some writers so much they came up with the 'Imaginary Story' so that they could have their cake and have Luthor poison it to death with Kryptonite too.
The invention of super hero comics that were considered even less real than the usual monthly adventures of a space alien who looked just like a beefy white dude and could melt things by looking at them and fly, or the nocturnal adventures of a rich orphan and the teenager in hot pants he kept around to distract psychotics helped stave off the authorial lust for blood for a while. But it couldn't last forever.
The first death I really remember in comics is the death of Ferro Lad.
Ferro Lad, a member of the 30th century Legion of Super Heroes, sacrificed his own life to save Earth from an alien creature called a Sun Eater, which yes, ate suns. Ferro Lad's death was a very rare event in comics at the time, the death of a heroic figure, even if he was more famous for dying than he was for anything he did while he was alive.
It's interesting to note that in death Ferro Lad became more famous and respected as a Legionnaire than he ever would have been had he lived. On the other hand he didn't have to call him self "Sir Prize" or have Proty as a pet either. Ferro Lad's death became one of a select few deaths in comic books that seemed relatively inviolate, like that of Captain America's partner Bucky or the X-Man Thunderbird, more or less heroic deaths onscreen (so to speak).
At the same time that this process was underway, we also had the introduction of more 'realism' in comic books. Super heroes could have troubles with money, with women... in short, 'realism' effectively meant 'We're going to make these bastards suffer like a modern day Job'. Marvel Comics pioneered this trend with comic books showing the Fantastic Four going bankrupt, Spider-Man's relentless drumbeat of financial and personal calamity (your aunt is dying because you gave
her a blood transfusion and you have radioactive blood and did we mention that you're trapped under a giant machine?) as just two examples. Writers in the 70's and 80's who wanted to live up to this kind of pressure to make life suck eventually just had to kill somebody.
In 1973 (I was two) Gerry Conway did it. He killed off Spider-Man's girlfriend Gwen Stacy.
Apparently, he did this because the writers didn't want to see Spider-Man get married, believing this would age the character too far from his roots as a troubled teenage character. This makes sense in the strangely static, status-quo enshrining milieu that is the superhero comic book. While it is true that as the decades pass changes are made to characters (for instance, the modern Batman would not be as quick to shoot people as he was in the 30's, as the character did not yet suffer from his now infamous aversion to firearms) the comics medium in general tends to return to certain core tenets and achieves a sort of equilibrium as a character gains more history. At the time Gerry Conway was writing the death of Miss Stacy, he was one of only a few people to write a Spider-Man comic book following the departure of the character's co-creator Stan Lee. He was, effectively, blazing a trail for how comic books would handle the idea of real, lasting change, and his decision (supported by the editors of the time) was to deal with it by killing Gwen before it could happen.
Ironically, this did indeed prevent one kind of change... Spider-Man would not be a comic book starring a married man for another decade or so... but caused quite another. The semi-innocence of the Silver Age died alongside Gwen, as the men and women who were now taking the reins of storytelling at both Marvel and DC (and who had spent the previous decade reading the comics themselves) became both more insular and more willing to go to extremes to prevent the comics from falling victim to 'change'. Gwen's death was followed hard-upon by that of her killer, Norman Osborn/The Green Goblin, and we wouldn't see him again for another 300 issues of the comic.
Yes, that's right, his death was so final (he impaled himself on his own rocket powered glider in an attempt to kill Spider-Man, and we saw him die right in front of us, not a dream, not a hoax, not an imaginary story) that it lasted almost two decades. That kind of death is almost unheard of in comics nowadays, however.
The result of the constant brinkmanship between those who wanted to change things and the inherent status quo of the medium led to more and more shocking deaths, deaths that happened 'in front of the camera' or more accurately on the very page. While villains could still get away with You Never Saw The Body, the 70's and 80's became a much more uncertain time for the friends, family and even the superheroes themselves.
The ultimate manifestation of this trend was Marv Wolfman's Crisis on Infinite Earths. Not even counting an infinite array of universes which all died before page 1 of the miniseries, we have a heck of a death toll in this comic.
Without even going to pick up the trade, I can list Psimon of the Fearsom Five, Kole, Dove and Aquagirl of the Teen Titans, the Red Bee (hah, the Red Bee died way before this, I just like mentioning the poor guy), The Red Tornado sorta (I'm not sure what Marv intended here), Peacemaker from the Charlton books, someone in a Green Arrow costume (I have no idea who that guy was, as it was the old costume), and of course the Flash (Barry Allen) and Supergirl (Kara Zor-El). Also some of the Global Guardians die in one panel or even off panel because Marv had a lot to cram in here.
Now, I've written at length about Crisis before and I expect I will again (for now, let me just say that never before or since has a comic book looked so good, been such a fun read, and yet totally screwed up an entire publishing company for more than two decades the way Crisis did) but here, the real effect of all these deaths ceases to be shocking or astonishing and just becomes tedious after a while.
Seriously, when the Earth 2 Robin and Huntress, the daughter of the Earth 2 Batman and Catwoman, die along with Kole it's all I can do not to yawn at this point. Whoopee, they died, so what? They didn't even have lives anymore anyway, thanks to Marv's relentless meat cleavering of everything fun and interesting about the DC multiverse concept.
After Crisis, comes the deluge. In this case, the deluge of 'reboots'. Oh, all the colors of the rainbow. And in this age of rebooting (which coincidentally comes around the same time as the one - two hammerblows of Watchmen and The Dark Knight Returns) we see whole periods tossed out in an attempt at making comprehensible the fevered dreams of a four color medium, and hoo boy do we see death.
I won't say it was all bad... John Ostrander wrote Suicide Squad, and that was a damn fine comic... but in general, the 80's and 90's were the time of blunt force trauma applied to comic books. Spines were broken over knees (the guy who broke Batman's back actually looks like a Mexican Luchador) and Superman actually died, killed by a rip-off of the Hulk.
Green Lantern went evil and killed his own comic book, and then a new Green Lantern came around just in time to give us all the concept of 'fridging' as his girlfriend of two issues is killed and her body jammed into a refrigerator for no other reason than to shock us. It fails, of course, because by this point what's left?
All of this would be bad enough if not for that status quo I mentioned. See, sure, you can break Batman's back and have someone else dress up in the costume in order to make some weird sort of morality play about how bad it would be if someone like Batman killed people while shooting bat shaped ninja stars.
Sure, Superman can die and be replaced by a teenage boy, an alien machine that acts
like Mack Bolan, an eeeeevil cyborg one step away from a swipe of Reed Richards, and an african-american guy drawn by Jon Bogdanove, who had at this time mastered the art of making me stare at the comic book in shock and horror at character designs that seemed more appropriate for Song of the South than a superhero book. But eventually, even if you kill off Aunt May and tell us that Spider-Man is in fact a clone of himself, things have to get back to the status quo, because the status quo is how you explain the comic book to people who haven't bought it yet and want to know what it is about.
Go ahead, try and break the Clone Saga down for a new reader who doesn't know who Spider-Man is. I'll wait. You want some help?
Batman's first Robin, after fifty years, is too old to wear short pants? Fine, we'll let him grow up. He's now in his twenties (yes, a character that debuted in 1940 is now in his twenties, oh my, I'm shocked at the frenetic pace of comics) but we'll get another kid to dress up in the Robin costume. Amazingly, the fans don't like the new kid, especially after the writers decide to make him smoke and possibly kill people and in short, not act at all like Robin? Heck, most people reading the comic don't really get that it's a new kid anyway? Okay, then we'll let the readers vote to see if New Robin dies or not. Whoops! The readers have spoken, time to kill the New Robin. But that leaves us without a Robin!
Okay, so we get another kid to wear the costume. This one, we'll have act like Robin. Problem solved! Batman keeps his Robin.
So of course, Superman doesn't stay dead. We rebooted history, so now Ferro Lad doesn't stay dead because he never died at all. Hal Jordan (The Green Lantern who turned evil, not the one who had his girlfriend jammed into a fridge) dies instead of him, but he not only doesn't stay dead, he actually doesn't stay dead twice. The entire freaking Guardians of the Universe don't stay dead. Heck, that second Robin everyone voted to kill doesn't stay dead! Green Arrow gets his arm cut off, blows up, and is replaced by his own son, and even that doesn't stop him from being raised from the dead by the dead Green Lantern we mentioned before, just before that guy comes back from the dead all the way himself.
And now, twenty plus years later, the Flash who died in Crisis is coming back from the dead, while Supergirl (Kara Zor-El) is alive, even though it's completely incomprehensible as to whether or not she's supposed to be the Supergirl who died or not. Even the Multiverse is back: At this point the only people Crisis on Infinite Earths has managed to kill was the Red Bee, and he didn't even die in it!
When the Martian Manhunter recently died during DC's huge Final Crisis event (which I like to call Rock of Ages II: The Rockening) people outright wondered how long it would take for him to come back from the dead at his own funeral.
When your fictional universe has people betting on how long you stay dead, death has lost its sting. Marvel's no better: not only has Norman "I was impaled in the chest with a rocket" Osborn come back from the dead, he's now in charge of the US Government's superhuman regulation agency. Thor died twice and came back from Ragnarok. Several people who died were in fact Skrulls and are not dead after all, and while Captain America is still dead (although not for long), his sidekick turns out to have NOT died, so we have Bucky alive, a cyborg, a former Russian secret agent, and now Captain America.
Hawkeye died because of the Scarlet Witch, who then brought him back from the dead and had sex with him. Spider-Man's Aunt May died, turned out not to be dead, almost died again and was saved from death by the Marvel version of Satan when Spider-Man's wife Mary Jane Watson sold their marriage to him, because getting married ages Spider-Man too much, but deals with Satan are perfectly okay. I guess he forgot Uncle Ben when he was making deals with Satan, but on a happy accident note the whole deal brought his dead best friend Harry back from the dead too! Coming soon, DC Comics will be publishing a major summer crossover about people not staying dead, in fact.
The best career move a character in comics can make is to die at this point, frankly.