I'd actually put one in for Clint Eastwood.
Although most popular knowledge about him revolves around his earlier acting career (Westerns, Dirty Harry), you'll notice a distinct change in many of his films once he started directing.
* Play Misty for Me
* Breezy
* Unforgiven
* A Perfect World
* The Bridges of Madison County
* Midnight in the Garden of Good and Evil
* Mystic River
* Million Dollar Baby
* Changeling
* Gran Torino
* American Sniper
* Sully
* The Mule
Clint Eastwood didn't write any of those. He's an actor, director and producer of other people's work.
Not to forget
Letters from Iwo Jima
Flags of our Fathers.
He certainly took me by surprise by the depth of his offerings, given that I used to know him as blondie with no name and for dirty harry.
The American medium is film/TV. The Godfather is the great American novel. A story about immigrants moving to America and starting a family business.