Karellen is the only character to appear throughout the entire novel. He is the leader of the Overlords on Earth, and is known to humans as the "Supervisor." At first, Karellen only interacts with the Secretary-General of the United Nations, Stormgren, but after a generation he reveals himself and his fellow Overlords to mankind. Karellen's attitude toward humans is never one of superiority or contempt, despite the Overlords' immense technological and intellectual achievements. Karellen (and his fellow Overlords) actually seem to view the humans with pity. They can identify with humans such as Stormgren and George Greggson, humans who are still flesh-and-blood creatures like themselves. But Karellen also knows that humanity will eventually be utterly destroyed when this next step is taken, as a generation of human children suddenly become creatures of pure intelligent energy, part of an "Overmind" that criss-crosses the galaxy looking to add more races to its own form. There is something horrible in this, particularly in the way the rest of human society destroys itself while awaiting its children's bizarre armageddon. Karellen is trapped in his role as a supervisor, and it is his job to nudge the human race in the right direction until it reaches the necessary developmental stage. His motivations are simple: he has no choice but to obey the Overmind or presumably suffer some kind of consequences. But Karellen would do the job anyway, if only for the opportunity to examine the process and, perhaps, discover the secret to it.