Let's go back to the beginning. The first real Blondie movie was made in 1938. Blondie appears in various forms from Blondie of the Follies in 1932 to Bye Bye Blondie in 2010, neither of which had anything to do with our Blondie.
She started as a comic strip drawn by Chic Young in 1930. Her name was Blondie Boopadoop until 1933 when she married Dagwood Bumstead. This feels really silly to write, but it is all true.
Enter Penny Singleton (1908 - 2003). She is the quintessential Blondie, and Arthur Lake (1905 - 1987) was perfect as Dagwood. Penny wasn't really a blond, but she remained that way after she got the role. She was still blond when I met her in the 1980s. They made 28 Blondie films from 1938 to 1950. But we don't cover stars here. Let's look at the rest.
Husband and wife actors Kathleen and Gene Lockhart are both in Blondie. They worked together some 21 times. As I mentioned before, they are the parents of June Lockhart, famous for "Lassie" on TV. The three of them worked together on one film, A Christmas Carol in 1938.
Child actor Larry Simms (b. 1934) played Baby Dumpling in the Blondie series. He was also in Mr. Smith Goes to Washington (1939), It's a Wonderful Life (1946), and a few other films. I can't find much online about him. 28 of his 36 films were in the Blondie series.
Jonathan Hale (1891 - 1966) played Mr. Dithers, Dagwood's boss. He has 244 roles listed on IMDb starting in 1934 and into TV, with his last listed role on "Kraft Suspense Theater" in 1965. He was in Charlie Chan's Secret in 1936 with Rosina Lawrence. While he was making the Blondie series he also had a recurring role in The Saint series. He was a hard worker, making over 80 films in the decade of the 1940s.
Irving Bacon (1893 - 1965). He is another gold mine to be explored.
Bacon started making films in 1923 with the Keystone Studio and Mack Sennett. He made the switch to talkies and eventually to television. IMDb lists 515 roles to his credit. Yes, 515! He was in a dozen or so Blondie films, but look for him also in nine Frank Capra feature films. I recognize his face, but I doubt I ever heard his name.
Movies of this era are rich with the best in Bit Actors!