First appearance = Leading Comics #1 (Winter 1941):
Vigilante (Greg Sanders) first fought the Dummy in the first adventure of the Seven Soldiers of Victory (a.k.a. "The Law's Legionnaires").
The Dummy returned several more times to tangle with the Vigilante in his feature in Action Comics starting in issue #58 (cover-dated March 1943).
And from Who's Who: The Definitive Directory of the DC Universe Vol. VII (September 1985):