Some of his novels and stories were fantasies. By no means all of them were, and by no means all of the fantasies, however three of them have had a profound indirect influence on the twentieth century. Gladiator, about a mutant with incredible powers, was acknowledged by Siegal and Schuster to be an inspiration for Superman. In it a planet enters the Solar System and will encounter Earth. Earth's best and brightest are rounded up and put into a spaceship, and watch the collision from space.
Earth is destroyed.
Then they land on the other planet, which proves to be habitable. When Worlds Collide provided an inspiration for the very first pages of Flash Gordon, which appeared soon after. It also spawned a sequel, After Worlds Collide, where we learn about an extinct alien race which once lived on this world. I could go on and on because I am a Wylie fan. His last book which was a fantasy was also an episode of the old series Name of the Game.