If Childhood's End were a restaurant, then Rikki Stormgren would be its maître d'. He's the guy who introduces us to the setting, sets the tone for the evening, and shows us to our seats, so we can be all nice and comfy when the main entrée comes along.
And like any literary host, Stormgren plays two vital roles: exposition expert and trendsetter.
Yep, Stormgren plays the ever-unappreciated role of exposition expert. What's an exposition expert you ask? Good question.
Exposition is, more or less, background information. It's the stuff the reader needs to know to understand the story to come. Our dear friend Stormgren is the character to either think or receive this information, thereby hooking the reader up with it as well. Through him, we are able to integrate ourselves into this weird and complicated world where aliens rule with a subtle hand, and people have to live with giant spaceships hanging overhead. Here's an example of what we're talking about:
And very probably, thought Stormgren, Karellen was watching the whole thing and enjoying himself hugely, for this meeting would never have taken place except at the Supervisor's instigation. (2.11)
See, Stormgren has been dealing with the Overlords long enough to know that they can see everything happening on Earth. He only thinks this thought so that we, the readers, can understand this fact.
Also, through this thought, we get to understand just how much power Karellen has over the Earth. Stormgren is the Secretary-General of the U.N., after all, so Karellen must have some serious influence to be able to pull his strings.
See how much information we got out of that thought? And it's just a single sentence long. Put together enough chapters filled with sentences like that, and you can see why we call Stormgren the exposition expert.
When you think back to old-timey science fiction films, chances are you imagine the main character as a cliché scientist. He wears a lab coat, talks about sciencey things with his colleagues, and uses his vast knowledge of his field to ultimately defeat the giant monster or creature from the black lagoon or whatever.
Stormgren is basically that character, only he doesn't wear a lab coat.
For example, after being kidnapped, Stormgren decides he wants—nay needs—to know what Karellen looks like. His curiosity and desire to learn about the unknown is far too great for him to live happily without it. So, he has Pierre Duval create a device for him to enable him to sneak a peek at Karellen through the two-way mirror. The result:
Yes, Karellen had trusted him, had not wished him to go down into the long evening of his life haunted by the mystery he could never solve. (4.160)
While most people might have been irked at not solving the mystery of Karellen, Stormgren would have been "haunted" by the prospect. And this desire to solve for x is what makes a scientist a scientist, and a key trait Stormgren shares with them. He's a scientific character through and through—even though he works at the U.N.
We call Stormgren a trendsetter because the main characters that follow in Acts II and III will have these traits, too. Jan Rodricks's desire to explore the unknown will also force him to have to trick Karellen, while Jeffrey's search for something new and unknown will cause him to be the first child to begin the transcendence into the Overmind.
Stormgren sets the trend in the novel that the main characters will have a scientific outlook on life and will act and think with reason and rationale.
Now please enjoy your meal.