His enemy is the Purple pretender Eric Ulnar, who sought the Medusae out in the first place, seeking to become the next Emperor of The Sun. One of the Purples, John Ulnar, supports the Legion from the start, and he is the fourth great warrior. But the Medusae, who are totally unlike humans in all ways, turn on the Purples, seeking to destroy all humans and move to the Solar System, as their own world, far older than Earth, is finally spiraling back into Barnard's Star. The renegade Purple pretenders ally themselves with the Medusae as a means to regain their empire. The Legion itself is the military and police force of the Solar System after the overthrow of an empire called the Purple Hall that once ruled all humans. The Legion of Space warriors of the 30th Century battle the Medusae. The Medusae cannot speak, but communicate with one another via microwave. They spoke of a gigantic planet, the lone planet of Barnard's Star, populated by ferocious animals and the single city left of the evil 'Medusae.' The Medusae bear a vague resemblance to jellyfish, but are actually elephant-sized, four-eyed, flying beings with hundreds of tentacles.

The story takes place in an era when humans have colonized the Solar System but dare not go farther, as the first extra-solar expedition to Barnard's Star failed and the survivors came back as babbling, grotesque, diseased madmen. Williamson may have been influenced by the similar device which Edgar Rice Burroughs provided for The Moon Maiden and The Moon Men a decade earlier. The series employs the plot device of the false document, purporting to have been written by a 20th Century American capable of experiencing the lives and adventures of his remote descendants in future centuries and writing them down. Jay Kalam (Commander of the Legion) and Hal Samdu (an anagram of Dumas) are the names of the other two warriors. In his youth he was called Giles The Ghost. He was once a criminal, and can open any lock ever made. The Falstaff character is named Giles Habibula.

Williamson took this idea into science fiction with The Legion of Space series. While attending a Great Books course, Williamson learned that Henryk Sienkiewicz had created one of his works by taking the Three Musketeers of Alexandre Dumas and pairing them with John Falstaff of William Shakespeare. 20th Century Golden Age Science Fiction - Jack Williamson's Legion of Space Series Book 1: THE LEGION of SPACE From Wikipedia: _ The Legion of Space is a space opera science fiction series by Jack Williamson.

The Legion of Space by Jack Williamson