doo-dah man
Literally, a backup singer who harmonizes with doo-dahs, doo-wops, shoop-shoops, sha-las, and the like--a minor figure, definitely not the lead singer. By extension, not the boss, kingpin or ringleader, but someone in the background, who "sings along", supports, assists, abets or worse.
The Chairman was calling the shots--everyone else was a doo-dah man.