They sing songs, typically written by other people, on records (except Marvin, he wrote songs himself).
This is why I chose Miles Davis.
However, while I was writing this I remembered that Marvin Gaye composed the music for the movie "Trouble Man" (My favorite track being "T Plays it Cool"). I didn't remember him playing instruments on it though (I know Trevor Lawrence played the alto and tenor sax and Gene Page handled the string arrangements). I did mah googles and it turns out Marvin played piano, drums, and was the man behind the Mini Moog that was featured on it.
Marvin was a musician.