There was somebody who used to run ads in print magazines, when cassette tapes were a thing, touting the world's best lecturers on a variety of topics.
I've been listening to TTC for decades. Prior to MIT and others opening up courses online it was the only way someone like myself could get access to anything like that.
In the office, Michael Scott is asked to give a lecture and brings a boombox with the same music the TTC lectures start off with. Its a hilarious in joke if you get the reference.
I think this may be them:
https://en.wikipedia.org/wiki/The_Great_Courses
https://web.archive.org/web/20090714005930/http://www.nytime...
Looks like they have adjusted, but used to provide videotapes and cassettes.