Ballantine wanted to publish "Childhood's End" before "Expedition to Earth" and "Prelude to Space", but Clarke wanted to wait. He felt that it was a difficult book to release. He had written two different endings for the novel and was unsure of which to use. According to biographer Neil McAleer, Clarke's uncertainty may have been because of its thematic focus on the paranormal and transcendence with the alien Overmind. While the theme was used effectively by Clarke in the novel, McAleer wrote that "it was not science fiction based on science, which he came to advocate and represent". When he wrote "Childhood's End", Clarke was interested in the paranormal, and did not become a sceptic until much later in his life. Ballantine convinced Clarke to let them publish "Childhood's End" first, and it was published in August 1953, with a cover designed by American science fiction illustrator Richard M. Powers. "Childhood's End" first appeared in paperback and hardcover editions, with the paperback as the primary edition, an unusual approach for the 1950s. For the first time in his career, Clarke became known as a novelist.