Having mentioned Billy Dee Williams, I should point to his most well known pre-Star Wars role- in the telefilm Brian's Song, with James Caan.
While a solid film, it does slip into some maudlin moments when the Brian Piccolo character dies, Williams is terrific as Gale Sayers, star running back for the Chicago Bears.
Here is a highlight:
And here is the theme song that is one of the most famous in tv history, by Henry Mancini (who else?):
There's a reason it was called Brian's Song, after all.