Billy Strayhorn

Over time, the jazz classic Take The 'A' Train has evolved into the signature tune of Duke Ellington and his Orchestra, and to this day most people would probably say it was a Duke composition. It was actually written by Billy Strayhorn, an extraordinarily gifted pianist / composer, and a member of Ellington's band for three decades until his unfortunate demise from cancer in 1967.
The precise roles these two musical geniuses played in the creation of some of the world's greatest jazz is still unclear, but it has been said that Billy Strayhorn was the true creative energy behind Ellington's magnificent orchestra.
I can't really comment on that .......... but it does seem he is still largely hidden by The Duke's giant shadow.