Leto I (the first) was Paul's father, the Duke
, until being forced into taking up the fief
of Arrakis by Padishah Emperor Shaddam IV
It was Leto II, Paul's son, that became the God Emperor of Dune for about 3500 years after accepting the sandtrout skin, slowly metamorphosing him into a sandworm. The populace rather looked upon him sort of like they would Shai-Hulud (the Fremen word for a sandworm deified). He also led humanity upon his Golden Path.