The Ding Dong Daddy was a real person, a streetcar conductor, who became famous for bigamy during WWII. The man was Francis Van Wie, a 58-year-old street car conductor, aka The Car Barn Casanova, aka The Ding Dong Daddy of the D-Line. (Although he actually worked on the 22 Fillmore Line, D Line sounded better.)
A popular but fanciful song was written about him.
Here's a link to a newspaper article on him:
https://www.sfexaminer.com/news/the-ding-dong-daddy-of-the-d-car-line/