Man, when this baddie sits around a planet, he sits around a planet. (Learn Spanish: "Archivo!")
Sorry, gang, quick one tonight. Don't worry; while I may be concise (and who knows, I could end up being ridiculously verbose in the end-- these things tend to happen), I shall be especially insightful. Maybe.
Galactus is the most terrifying being in the galaxy. Also? He wears a skirt. Why? Because giant Jack-Kirby-created terrors from space have to wear skirts. It's the law.
I'm sure you all know about the Big G, but for formality's sake-- Galactus is a big ol' dude with a tall helmet who goes around eating planets, usually guided by a herald. He keeps trying to eat Earth, but the Fantastic Four and friends keep pushing him away. Because of this, Galactus suffers from diminishing returns, though some writers find clever spins-- such as having Galactus battle Ego, the Living Planet!
Basically, the idea behind the original Galactus story-- probably Stan Lee and Jack Kirby's biggest and best story in the Fantastic Four, and smack dab in the middle of their run-- was "the FF fight God." Of course, this is the Marvel Universe, so it's God that's the villain, and his fallen angel, Lucifer-- in this case, the Silver Surfer-- that's the good guy. It's a huge, cosmic, mythological extravaganza-- exactly the kind of thing Jack Kirby always brought us.
Nothing can beat classic Galactus. Sure, audiences in this day and age might think he looks silly, but that's because he does. He's friggin' Galactus, though, so he can pull the look off. Later generations have tried to reinvent him-- I'm thinking Gah Lak Tus and Stormcloudus here-- and they haven't nearly managed to capture the power and grandeur and ball-out craziness of the one true Galactus.