A tribute to one of the great radio/animation voice actors, Bill Thompson (Droopy, Smee, the White Rabbit, Wallace Wimple and the Old-Timer on Fibber McGee and Molly, Adolf Wolf in Blitz Wolf -- but not, as you'll find out, Fred Flintstone). Nobody could do a mush-mouthed voice as amusingly as Thompson; there was something so loveable and innocent about his timbre that any character became adorable when he used that voice, even if it was an evil pirate's assistant or a Tex Avery character.
The one thing that isn't answered here is why Thompson was so often unavailable to do the voice of Droopy. In the mid-'40s the answer was that he was in the service, but there were a bunch of cartoons in the late '40s and '50s where Thompson was replaced by Avery himself or by Daws Butler ("Deputy Droopy"). Even more oddly, once Michael Lah took over the Droopy series in 1956, Thompson was available for every Droopy cartoon until the studio shut down.
(Via Cartoon Brew.)