God Emperor of Dune

Arrakis, the barren desert planet, is now a green and hospitable world. The giant sandworms are gone and there is only one link between the world and its epic past: the grotesque figure of Leto Atreides, son of the prophet Paul Muad'Dib and now the virtual immortal God Emperor of the Galaxy because he holds the sole ingredient which confers longevity. But his final victory, to produce a species that can outwit him despite his prescient vision, means his own death.  Book 4 of series.