Allan Dwan was one of Hollywood’s most prolific directors, working from the silent era through the golden age of the studio system. The Toronto-born filmmaker made somewhere north of 400 films—many of them woefully obscure, unavailable, or lost—during his career, and in a variety of genres and registers. As a proverbial gun-for-hire, he could have turned his productions around with anonymous influence, with little or no authorial voice to distinguish his work from the myriad other filmmakers tasked with nominally similar projects.

And yet, the best of Dwan’s films—among them Frontier Marshall, Brewster’s Millions, Silver Lode, and Slightly Scarlet—evince a psychological complexity and stylistic self-sufficiency rare for such genre-oriented fare. If Dwan’s films can be categorized by their conventions, they likewise refuse to be reduced to caricature, often recalibrating symbols of American mythology—the cowboy, the criminal, the solider, the entertainer—as vessels for vocational,...