Known for his immense size and stomach powers, he is a cosmic diety, although he doesn't really serve any overseer function, just floats around the stars chompin on space rocks like a big gay purple Pac-Man god.
His dumb hat is ugly and stupid but I guess it's slightly better than being a stupid space cloud that doesn't mean anything. Seriously, that would be unimaginative and sloppy.
He is so lazy that he will sometimes enslave locals to serve as his personal delivery persons, surfing across endless skies on epic coffee runs. He may promise not to eat your planet, and he may even mean it at the time, but for his horrible hunger; that sickening addiction will take him in a vicelike grip of unstoppable gravitational force, and Galactus will forget all about your puny mortal concepts like 'keeping a promise not to destroy all that you or any member of your species has ever known and loved'.
Stupid Galactus. I hate that guy. If he ever comes round here again I'm kicking his ass.