chairman of the board noun the most important person of a set of people Probably extended from its use as a nickname for Frank Sinatra, 1915–98 US.
You’ve got your big fook-off minders, your drop-dead gorgeous backin’ singers, your wasted, monged-out old musos ... an’ then me, right in the middle, the Boss, the Man. The Chairman o’ the fookin’ board. — Ben Elton, HighSociety, p. 216, 2002