The Buck Rogers comic strip had been very commercially successful, spawning novelizations and children's toys, and King Features Syndicate decided to create their own science fiction comic strip to compete with it. At first King Features tried to purchase the rights to the John Carter of Mars stories by Edgar Rice Burroughs; however, the syndicate was unable to reach an agreement with Burroughs. King Features then turned to Alex Raymond, one of their staff artists, to create the story. One source for Flash Gordon was the 1933 novel by Philip Wylie, When Worlds Collide. The themes of an approaching planet threatening the Earth, and an athletic hero, his girlfriend, and a scientist traveling to the new planet by rocket, were adapted by Raymond for the initial storyline. Raymond's first samples were dismissed for not containing enough action sequences. Raymond reworked the story and sent it back to the syndicate, who accepted it. Raymond was partnered with ghostwriter Don Moore, an experienced editor and writer. Raymond's first Flash Gordon story appeared in January 1934, alongside Jungle Jim. The Flash Gordon strip was well received by newspaper readers, becoming one of the most popular American comic strips of the 1930s. Like Buck Rogers, the success of Flash Gordon resulted in numerous licensed products being sold, including pop-up books, colouring books, and toy spaceships and rayguns.