Lucas wrote (or cowrote) Apocalypse Now. Had long planned on directing it but Star Wars got in the way. He and Coppola had a long working relationship together through American Zeotrope, both encouraging each other (and competing) in their respective projects. You can't tell the story of Lucas without talking about Coppola. A lot of this is detailed in Droidmaker. [0]

[0] https://www.droidmaker.com/