Mr. Belvedere: Exactly the same as the plot to the TV show. Mr. Belvedere is a butler who shows up to a slovenly family and turns them into perfect WASPs. He writes in his diary, which becomes a best selling book, and he leaves on a lecture tour about etiquette.
Mr. Belvedere Goes To College: Mr. Belvedere decides to serve as butler for a frathouse. He teaches them boring life lessons and so forth.
Mr. Belvedere Rings The Bell: Not originally a Mr. Belvedere script, it was about a random hobo settling into an old folks home and giving them the will to live. The studio decided to remove the main character and replace him with Mr. Belvedere with some bookends about Belvedere's book tour being cancelled.
Also he had a ton of books and short stories. THIS I DID NOT KNOW.