Jamie Madrox aka the Multiple Man.
Throughout Peter David's second X-Factor run (from 2005) Jamie is basically the main character of the book and goes through a ton of shit, some fairly traumatic. Yet by the end he gets what is basically the closest you can possibly get to an ending for a non-cape character, retiring on a farm with his wife and has a kid on the way. Legitimately one of the most satisfying character endings you're going to see in an American comic book.
...so of course, fast-forward a few years and he gets killed off to raise the stakes of a shitty post-Secret Wars X-Men event. But the hitch is that he died in a different location than the place he retired to, so the obvious way to bring him back is to be like surprise! the Jamie Prime and his wife are still happily retired and only his duplicates were killed. Even poor Peter David brought that up, presumably pissed that they did what is really his character so dirty.
Then last year we got the Multiple Man mini by Matthew Rosenberg, where the plot tries to be a little too clever for it's own good, but tl;dr there's a new Jamie Prime who's actually a dupe of a dupe of the original Jamie that survived in a bunker since before the events of X-Factor even began! Keep in mind this makes absolutely no sense at all, as it's established that if the original Jamie is dead the dupes also eventually die, but whatever.
So the original Multiple Man, the one that went through the entirety of the run that turned into a legitimate character is permanently dead and has been replaced by a clone! And none of the X-Men or even his wife have any issue with this. Seriously his wife is like "it's fun learning my husband again" while interacting with a clone that had literally never met her and didn't go through any of the stuff that brought them together in the first place! And Matthew Rosenberg really wants us to believe that it's the same character, despite the fact that it's explicitly pointed out in X-Factor how the life experiences of Jamie dupes can turn them into different people, meaning there is no possible way that this new Jamie should be anything like the old one.