This is really sad news. It's hard to say whether he was best known as a singer, actor or a civil rights activist because he excelled in all three fields. The last time I saw him on screen was in the brilliant film BlacKkKlansman (2018) and although he had relatively small role, he was really good in it. He was one of those actors who is able to draw your attention whenever he was on screen.
My favourite film of his is Carmen Jones (1954).