I am with you. The Thin Man: first major film franchise?
But my favorite WP is Life with Father with Irene Dunne.
You got it. You are probably right, The Thin Man may well have been the first full blown film franchise, will have to look that up. Still mt favorite film I love just about anything William Powell was in, never got a award for anything. He was certainly the best dressed,his clothes would be in style today.