Green’s Dictionary of Slang

(US tramp) one who pimps his own wife.

1927		‘Jargon of the Und.’ in DN V 447: Gagger, One who prostitutes his own wife.
1931		Irwin Amer. Tramp and Und. Sl. 82: Gagger.—One who lives on the earnings of his wife; or one who forces his wife into prostitution, such an action being enough to make the average man, tramp, criminal or otherwise, ill.