Dune (novel)
The desert planet Arrakis has been terraformed into a lush forested biosphere, except for a single section of desert retained by Leto for his Citadel. All of this he has done in accordance with a prophecy divined through precognition that will establish an enforced peace preventing humanity from destroying itself through aggressive behavior.
He has rendered the human population into a state of trans-galactic stagnation space travel is non-existent to most people in his Empire, which he has deliberately kept to a near- medieval level of technological sophistication. The Fremen have long since lost their identity and military power, and have been replaced as the Imperial army by the Fish Speakers, an all-female army who obey Leto without question. Leto has disbanded the Landsraad to all but a few Great Houses the remaining powers defer to his authority, although they individually conspire against him in secret. As a result, his rule is one of religious awe and despotic fear. Leto has been physically transformed into a worm, retaining only his human face and arms, and though he is now seemingly immortal and invulnerable to harm, he is prone to instinct-driven bouts of violence when provoked to anger.
The death of nearly all other sandworms, and his control of the remaining supply of the all-important drug melange, has allowed him to keep civilization under his complete command. Leto II Atreides, the God Emperor, has ruled the universe as a tyrant for 3,500 years after becoming a hybrid of human and giant sandworm in Children of Dune.