If you're not familiar with them, they were created in the 1970's, when the Marvel/DC rivalry was a little more petty. (In fact, DC tended to do Marvel parodies first, but very few of them stuck around because it's kind of harder to deconstruct Silver Age Marvel more than they do themselves. Also, I would argue DC's characters are little more archetypical). At first they were a handful of villains that vaguely resembled the Justice League, but then someone thought it might be fun to make an alternate reality with an alternate Justice League. Then, in the 80's, Mark Gruenwald did a miniseries about them which was sort of a proto-Watchmen, which kind of sealed their popularity as a way to do stories about iconic heroes without having to worry about upsetting the apple cart too much.