Kenny Delmar's character Senator Claghorn from
Fred Allen's radio show was the inspiration for the blabbermouth rooster voiced by
Mel Blanc. The public now knows the Warner Bros. cartoon character far better than the original.
Robert McKimson claimed the inspiration for Foghorn Leghorn came from the sheriff character on a radio show called Blue Monday Jamboree. That may be, but Blanc and the writers of his dialogue were obviously drawing on Delmar; and that is the connection made by audiences of the day.
Foghorn Leghorn betrayed little or none of the Senator's Southern chauvinism, but did retain his accent, speech patterns, tendency to bluster and the catchphrases, "That's a joke, son!" and "Pay attention, boy!"
Source:
Leonard Maltin, Of Mice and Magic: A History of American Animated Cartoons, NY, 1987, p. 259
See also: Blue Monday Jamboree on Radio Archives
And:
It's a Joke, Son! (1947) (1947) on IMDb (this is the only movie to feature Sen. Claghorn)