Complex sentence: The Atreides leave Caladan for Arrakis, a barren desert planet populated by gigantic sandworms and the Fremen, a mysterious people who have long held a prophecy that a messiah would come to lead them to freedom.
Split into simpler sentences: The Atreides leave their homeworld Caladan for Arrakis, a barren desert planet populated by gigantic sandworms. The natives of Arrakis are called the Fremen, who are a mysterious people that have long held a prophecy that a messiah would come to lead them to freedom.