Superhero comics, particularly Marvel and DC, have a number of peculiarities that come from effectively being incredibly long serial works. You get the strange effect of having an ongoing setting that has been built up over the course of decades by a great number of authors. Individual characters can go through periods of wildly different characterization due to changing times, changing writers, and the demands of the company as a whole.
One of the most uniquely comic-booky of concepts is the retcon. Short for retroactive continuity, a retcon occurs when an aspect of established continuity is changed after the fact. You can into a lot of debate over just what counts a retcon. Is it any change to the past at all? Does it matter if it's done by the same writer who created the element being changed, or by a different writer?
I view retcons as story changes that actively modify past stories and directly contradict continuity as it previously existed. It's not a perfect definition, but mostly it works. Superman's return after his apparent death wouldn't be a retcon because he was never intended to stay dead; Barry Allen's return from the dead is, since his death was meant to be permanent.
What got me thinking about this is a series of retcons that have been going on over the past few years in Marvel Comics around Nick Fury and S.H.I.E.L.D. Specifically, Jonathan Hickman's Secret Warriors comic that ran from 2009-2011 and the current Original Sin event. Both have resulted in major changes, but where I ended up happy with Secret Warriors turned out, I've been more and more disappointed with Original Sin as it goes on.
I think in both cases a lot of the impetus has been a desire to bring the comic book versions of Fury and S.H.I.E.L.D. more in line with the movie version. Where movie Fury is Sam Jackson, the comic book Fury is a white guy who fought in World War II and became a super spy in the 60's. He's kept young by a serum called the Infinity Formula.
Without spoiling too much, Secret Warriors ended with Nick leaving S.H.I.E.L.D., breaking his triple-agent girlfriend out of prison, and riding off into the sunset. It was a great send-off that retired the character after giving him one more great story. I was sad to see Nick go, but I was okay with it.
Spoilers for Original Sin after this point.
Original Sin brought him back to reveal that he's been secretly murdering aliens and monsters for decades to preemptively protect Earth from them. The Infinity Formula wore off, so he's an old man now. He's apparently murdered the Watcher. And his best friend was actually killed in 1966 and all his appearances since then were actually a robotic replacement.
If the final issue of the story doesn't end with Fury dead, I'll be shocked. Everything about this story just feels like an attempt to not only ensure he's no longer usable, but also no longer liked. I'm sure once this is finished, it'll be a long time before we see him again. What makes me sad is that he was already set aside, but in a way that seemed appropriate to the character.
Eventually though, decades from now most likely, someone will decide they want to bring him back. And they'll do it, because in comic books death is never permanent. Just ask Barry Allen.