Flash Gordon is the hero of a science fiction adventure comic strip originally drawn by Alex Raymond. First published January 7, 1934, the strip was inspired by and created to compete with the already established Buck Rogers strip. Flash Gordon was featured in three serial films starring Buster Crabbe: Flash Gordon (1936), Flash Gordon's Trip to Mars (1938), and Flash Gordon Conquers the Universe (1940)
The first Flash Gordon serial remains copyrighted, but the compilation made of the second serial, and the third serial itself are in the public domain.
The plot for Flash Gordon Conquers the Universe is as follows:
A deadly plague is ravaging the Earth, known as the Purple Death because of the spot left on victims' foreheads. Ming the Merciless is suspected to be behind the plague and it is discovered that his spaceships have been dropping "Death Dust" in the Earth's atmosphere. Flash Gordon, along with Dr. Alexis Zarkov and Dale Arden, is sent to the planet Mongo to find a possible cure for the plague. They eventually find an antidote, called polarite in the Kingdom of Frigia. Flash and Zarkov distribute the antidote the same way the original Death Dust was spread. Ming sends an army of robot bombs after the three and he succeeds in capturing Zarkov for a short time before Flash frees him.
The trio continue to battle Ming and his allies. Ming's Captain Torch is the "head villain" of this serial. He is in charge of stopping the Earthlings. Before Flash and his team leaves, they kill Ming by locking him in a tower and crashing a rocket ship loaded with Solarite into it. Prince Barin takes his rightful place as ruler of Mongo. Ming's last words are "I am the universe!". Zarkov announces that Flash Gordon has conquered the universe. (Source: wikipedia.org)