Flash Gordon Conquers The Universe (1940)
One of the three serials made from 1936 to 1940, "Flash Gordon Conquers the Universe", finds our brave hero fighting the 'Purple Death', a mysterious plague ravaging Earth. Alas, planet Mongo and its evil ruler, Ming the Merciless, are behind the plot for conquest. So its back to planet Mongo for Flash, Dale, and Zarkov with allies Prince Barin of Arboria and Queen Fria of the frozen northern land of Frigia to put a stop once and for all to Ming and his evil ambitions.