Kubrick spent five years developing his next film, "2001: A Space Odyssey" (1968), having been highly impressed with science fiction writer Arthur C. Clarke's novel "Childhood's End", about a superior race of alien beings who assist mankind in eliminating their old selves. After meeting Clarke in New York City in April 1964, Kubrick made the suggestion to work on his 1948 short story "The Sentinel", in which a monolith found on the Moon alerts aliens of mankind. That year, Clarke began writing the novel "" and collaborated with Kubrick on a screenplay. The film's theme, the birthing of one intelligence by another, is developed in two parallel intersecting stories on two different time scales. One depicts evolutionary transitions between various stages of man, from ape to "star child", as man is reborn into a new existence, each step shepherded by an enigmatic alien intelligence seen only in its artifacts: a series of seemingly indestructible eons-old black monoliths. In space, the enemy is a supercomputer known as HAL who runs the spaceship, a character which novelist Clancy Sigal described as being "far, far more human, more humorous and conceivably decent than anything else that may emerge from this far-seeing enterprise".