Although it's always been relatively uncommon, legendary old-school blues musicians have let their voices and/or images be used to sell products in ads and commercials.
There's that semi-famous 1993 John Lee Hooker ad for Lee Jeans, for instance!
Still, this relatively new find is a total surprise. It's a clip of Muddy Waters doing a radio ad for Dr. Pepper.
According to the info posted along with the clip on YouTube, this is one of several audio ads from an series composed by Randy Newman for Dr. Pepper's radio campaign in the late Sixties or early Seventies.
Although Muddy is clearly singing Newman's Dr. Pepper-centric lyrics, It sounds like he's making up the melody as he goes along—as any great blues musician would do!
The top clip is Muddy's radio ad. The bottom clip is Hooker's Lee Jeans commercial, because we couldn't resist.