Bloom County was originally about Milo Bloom, a wisecracking kid in glasses, and his family with whom he lived in a boardinghouse. Then one day, supporting character Binkley got himself a penguin as a pet, and we all know what happened next: Opus eventually became the flagship character of the strip and Berke Breathed’s entire career.
Brainiac Five is, in that sense, the Opus of the Legion of Super-Heroes. After all, the Legion stories were originally the province of Superboy and his three friends Cosmic Boy, Lightning Lad and Saturn Girl – but for a very, very long time those three characters were all bland milquetoasts, and not simply because of the Silver Age’ tendency towards whitebreadiness: Rokk and Garth were both pretty bland for decades after their creation, and Imra only came into her own late in Paul Levitz’ run as “the one who was willing to go further to get the job done,” which is pretty basic but is at least a character note. Eventually – and primarily in the reboots – Rokk became Captain America of the Future and Garth became the hothead, and those three finally had personalities, but it was too late for them to reassert their prominence as the founders.
Mostly this was because Brainiac Five showed up. Brainy has become pricklier in recent years – the beginning of the reboot, where he was downright antisocial, was probably the apex of that – but the character, even in the Silver Age, has always had a streak of self-importance and ego that is nonetheless appealing because you have to admit he’s got a point: he really is the smartest superhero in comics, smarter than ten Reed Richardses put together, and if he occasionally loses patience with Element Lad you can’t blame him for that.
But also it’s appealing because you understand where Brainy is coming from. After all, his name is Brainiac Five: most incarnations of the character have established that he’s the “only good Brainiac,” with all of the other ones being evil universe-conquering android dictators. Despite being the engine for most of the team’s plans and ideas – when Brainiac Five is stumped, you know the team is really, really in trouble, because he’s their go-to guy for having a solution to whatever evil they have to beat – he’s always proven himself to be absolutely balls-awful at being the leader of the team.
It’s interesting, because most other characters who become “most popular” among fans (and Brainy is, at this point, far and away the most popular Legionnaire ever) eventually become the de facto leader of the team: see how Wolverine has grown from being just the team berserker into the respected elder statesman of the X-Men, to the point where the next X-crossover has him openly challenging Cyclops for leadership of all mutants everywhere. But despite the fact that the Legion’s greatest successes are all more or less driven by Brainiac Five and he’s the most popular character, he’s definitively not the leader of the team.
You can of course explain his popularity pretty easy: he’s the Batman of the Legion in terms of style, the thinker, the planner. Nerds always love thinkers and planners, because the idea of not having any superpower other than “I’m smarter than you” is one most nerds imagine themselves to already have. But he’s usually also the idealist: the guy who refuses to exploit the Metal Men once he realizes they’re sentient. Nerds like that too. He’s surpassed being a bit of a social outcast, but is still clearly his own man: nerds like that as well. And he gets to be a bit of a sarcastic dickhead and get away with it because his smarts are so necessary, and you’d better believe nerds love that idea. You can make an argument that Brainiac Five is in many ways the ultimate mirror for nerd self-flattery…
…except, of course, that he’s got a history of mental instability.
…and his greatest failure – being unable to save Supergirl, the woman he loved – puts the lie to his “I can solve any problem” reputation.
…and he’s quite clearly unhappy most of the time.
That’s why Brainiac Five is such a great character: he takes all of those nerd fantasies, embodies them, and then destroys them by demonstrating their irrelevance. It doesn’t matter that he once temporarily destroyed the embodiment of a conceptual end of the universe by smashing it in the face with a different conceptual embodiment of the end of the universe: at the end of the day he’s still, all things considered, a very sad person. And that’s a pretty great thing.
(Also: I love super-smart characters because they can engage with essentially anybody and be ready for it. You just know that Brainy knows of the existence of the Endless, for example. He might be irritated that they exist, but he can handle the idea that vague concepts can be personalized. Wouldn’t you love to see him chat with Destruction some time?)