"I---I can't turn invisible fast enough!! How can we stop this creature, Torch?"
"Just wait and see, sister! The Fantastic Four have only begun to fight!"
"The three of you can't do it alone! It's time for The Thing to take a hand!"
"It'll take more than ropes to keep Mister Fantastic out of action!"
Among its many other important accomplishments in comic books, Fantastic Four #1 had a distinctive cover, featuring the Mole Man's large, green creature, bursting out of the ground, holding Susan Storm in one hand while the other three members of the Fantastic Four fight it, all while loudly demonstrating or explaining their powers. Speech bubbles on comic book covers are usually not seen as a good aesthetic and marketing point, but these lines of exposition have become somewhat of a classic.
The cover is well-composed, especially seen through the mind of a 12 year old in 1961, deciding how to spend that precious dime. We have a monster, popping up out of the ground, and then once that immediate danger has been established, we have four figured radiating out from it, all with different powers. If someone was curious, the dialogue would cue them into what was happening, and even give hints about more drama developing: two of these people are siblings, for example.
For these reasons, and also because of Fantastic Four's obvious importance in general, the cover of Fantastic Four #1 is one of the most common covers to be the subject of homage, tribute and parody, with a good selection of these covers viewable here. Along with Action Comics #1 and Amazing Fantasy #15, the cover of Fantastic Four #1 is probably one of the most familiar, and referenced, comic book covers, to comic book fans, and perhaps to parts of the general public.