Novelization
After the film was released, a novelization quickly followed in both hardcover and mass-market paperback; it was written by W. J. Stuart (the mystery novelist Philip MacDonald writing under the pseudonym), which chapters the novel into separate POV narrations by Dr. Ostrow, Commander Adams, and Dr. Morbius. The novel delves further into the mysteries of the vanished Krell and Morbius's relationship to them. In the novel, he repeatedly exposes himself to the Krell manifestation machine, which (as suggested in the film) boosts his brain power far beyond normal human intelligence. Unfortunately, Morbius retains enough of his imperfect human nature to be afflicted with hubris and a contempt for humanity. Not recognizing his own base primitive drives and limitations proves to be Morbius's downfall, as it had for the extinct Krell. While not stated explicitly in the film (although the basis of a deleted scene found on the film's 50th anniversary DVD), the novelization compared Altaira's ability to tame the tiger (until her sexual awakening with Commander Adams) to the medieval myth of a unicorn being tameable only by a virgin.
The novel also clarifies an issue only hinted at in the film. When Dr. Ostrow dissects one of the Earth type animals, he discovers that its internal structure is altogether unlike that of any real animal. The tiger, the deer, the monkey are all conscious creations by Dr Morbius and only outwardly resemble these creatures. Since the Krell's Great Machine can project matter "in any form", it can create life. The Krells' destruction was, in part, punishment for appropriating the powers of God. This is why Commander Adams says in his closing speech "...we are, after all, not God".
Anthony Boucher dismissed the novelization as "an abysmally banal job of hackwork." Others rate the novel as being a fitting accompaniment to the film.
Read more about this topic: Forbidden Planet