Dr. Demento is the stage name for Barry Hansen, a Los Angeles-based radio personality who specializes in playing records of novelty songs and parodies of pop music from all eras. I became familiar with his radio show while living in California in 1974. His show was on Sunday evenings, and I was a faithful (more or less) listener each week.
There were a few times when I called the show to request a favorite novelty or comedy record I'd remembered from years earlier, and sure enough, he had all of those in his massive collection. But there were some obscure records he didn't have, and in 1975 I wrote him, offering to make audio cassettes of those that may be of interest to him.
He replied with this letter and photo. I did make the cassettes for him, and requested a few songs in return, which I never did receive.