Green’s Dictionary of Slang

a joc. corruption of SE manager, implying the alleged effect on those whose livelihoods are in his hands.

1897		Windsor Mag. 6 126/2: He began to laugh, and to say they mustn’t lose that 7.30 to London, or the ‘rag’ would be rolling up without her and the ‘stage damager’ would be using ‘cuss words’.
a.1909		press cutting in J. Ware Passing Eng. of the Victorian Era 103/1: The green room became so crowded that at last the damager was compelled to put up a notice.
1913		H.G. Van Campen ‘Woes of Two Workers’ in McClure’s Mag. Aug. 192/1: The stage damager’s been sore on me ever since I ast his wife [...] if the lady he was ridin’ in the Park with last Sunday was her sister [Ibid.] 198/1: The damager says to me this mornin’, ‘You’re allus tryin’ to roll up a revolution,’ he says.
1924		(con. 1890s) J.B. Booth Old Pink ’Un Days 294: And it was the Stage Damager [i.e. Charles Harris] who made an immortal addition to the rules of Court etiquette during a rehearsal of a costume play.
1969		S.T. Kendall Up the Frog 13: ’E said ’e was the damager an’ give me ’is Wilkie Bard.
1977		D. Powis Signs of Crime 180: Damager Manager (boxing and theatrical use also).
1984		(con. WW2) T. Jones Heart of Oak [ebook] The civvy NAAFI manger, the ‘damager’ as we called him.