I was one of those who only knew of him from the singing of "Old man River" until I got involved in the Glasgow folk scene.
I was told this story by Danny Kyle, sadly dead a few years now but he told of Paul robeson being booked to do a concert at Glasgow City Halls but at around that time his passport had been revoked, debarring him from leaving the US. There was an obscure American radio station which somehow set up a Transatlantic hook-up and the show was broadcast live to a packed hall (capacity c. 2000, I think) and all that was on stage were some speakers... Never found out if it was true or apocryphal...
I've also been told of him playing in Glasgow Bellahouston park, once he was free to travel again, to some 50,000 people and have seen the photos.

To add to the sense of continuity, I was working a couple of years ago with a girl in her early 20s, who was a huge fan of him, because as she was growing up, her mother had played him on old, now treasured and very worn, cassettes. She in turn pointed me to a recording by the Manic Street Preachers (who said peolitical song isn't popular?) entitled "Let Robeson Sing" No prizes for guessing the context....

Andy