I'm not sure who invented the idea of a "variant cover" for comic book issues but I recall it was something that gained prominence in the 90s to try to prop up sales. Because you couldn't reboot your series every month or "kill" and then resuscitate your character every month. The idea is that you have the same issue of a comic book but there are different covers. TV Guide used to do that too sometimes. That way obsessive (or idiotic) collectors will go out and buy the same issue multiple times to get all the covers. And then...profit--at least for the publisher. For the collector, not so much.
Maybe it's just me, but this seems to be happening a lot recently. DC has been doing it a lot, mostly because they're getting their ass handed to them by Marvel. What they've been doing is they'll recruit some legendary old artist and then have him draw covers for a month for all their comics Or with The Dark Knight Returns III (Or I guess Dark Knight Re-Re-Returns, right?) they have a whole shitload of different artists each do a variant cover to the tune of 52 or so. I don't feel like looking up the real number but it's something completely obscene.
Of course other publishers do it too. I saw an article about a new Power Rangers comic that has 16 different variant covers. The article posed the question: are you going to buy them all? Um, no, because I'm not a fucking moron. Even if I had a job and more than $500 in my bank account I wouldn't waste my money buying the same goddamned comic book 16 times. Sometimes they would do variant covers that would all form a picture, which I guess you could at least display those, but what's the point of buying 16 completely unrelated covers? It's freaking stupid.
I suppose some people do it because they're OCD and just need to have every single issue. Others are under the false impression that these covers will actually be worth something. But when you print a million of each variant and these obsessive collectors put them right into a Mylar bag, you know what those covers are worth: nothing. The old comics like the first appearance of Superman, Batman, Spider-Man, etc are worth a lot of money because they're rare. Kids read them and their moms threw them away so there weren't that many left. These variant covers are probably never going to be rare because they printed a shitload and most of the people who buy them aren't going to throw them away. You know who pretty much said all that? Stan Lee! Seriously, it was in the 2003 History Channel documentary Comic Book Superheroes Unmasked referring to the "comic book bubble" of the 90s. But since comic book companies, like Wall Street, don't learn from history, they're blowing up another bubble that's bound to burst when these geeks realize that these variant covers are worthless. But, hey, they probably look real pretty in their Mylar bags.
Of course when I mentioned this on Facebook, comic book geeks were just like, "Whatever. You're a jerk. I can waste money if I want!" Personally I think like the lottery it's pretty much a tax on stupidity. I suppose the silver lining is it helps to prop up the comic book industry, which like newspapers and magazines face declining circulation.
Really though if you want to do something more worthwhile with your money, you can donate it to me. I'll put it to much better use.