The list of artists who have performed at Harlem's Apollo Theater reads like a Who's Who of black American entertainment. No black performer, from Sammy Davis Jr to Charlie Parker , could be considered a star without conquering the Apollo's tough, sophisticated audience. Tonight and next week Arena celebrates the 50th anniversary of the Apollo. But it is more than the story of a single venue. It is the story of Harlem itself and the struggles and triumphs of black America. Tonight's programme begins with the Apollo's infancy, when Bill (Bojangles) Robinson tapped effortlessly to the music of Fats Waller, and royalty like Count Basie and Duke Ellington held court.