Roy Rogers positively glows in this rousing action-thriller, which is really a Western only by a nip and a tuck, and in places has much more in common with the very best of the studio's cliffhanging serials. Nazi saboteurs appeared frequently, if rather incongruously, on the Hollywood prairie during World War II, but as played by Gerald Mohr (whose pencil-thin mustache immediately gives him away) and James Bush, they actually fit in nicely this time around. Smiley Burnette was inherited from the disbanded Gene Autry unit at Republic, but although usually strictly a matter of taste, the hayseed comedian does good work in King of the Cowboys. As do Dorothea Kent, a tough-looking, tough-talking blonde rarely seen in such rural surroundings, and heroine Peggy Moran. The latter discovered that she was pregnant during the making of this film and retired for good soon after, a loss for Hollywood in general if not, perhaps, for her husband, Universal director Henry Koster.